Unfortunately, we do not know. If one accepts that an individual at least inspiring Arthur as fact, it isn't hard to accept that he may have carried a named sword, perhaps a sword to which tradition had ascribed mystical powers. Arthur would be only one of thousands of historical generals/warlords/kings/warriors to ascribe a personal name to his weapon of choice, particularly in the Northern European military tradition. There's nothing unusual about him carrying such a weapon, if indeed one accepts Arthur as at least possible in an historical setting. If there was a "named sword" owned by the individual who inspired Arthur, then it is highly likely, based upon the excavation of other burials of the Late Roman/Early Dark Ages time frame, that Arthur was in fact buried with Excalibur, as it would have been a prized posession. If, however, the sword was a sort of tribal symbol of leadership, it is entirely possible that one of two scenarios might have played out: A) The sword was passed from leader to leader until being lost to history. B) The sword was captured by an enemy (presumably the enemy who slew Arthur, or a relative of the enemy who mortally wounded him), and was then taken as a war prize, never to be seen again. There are some who believe that Arthur may actually have been a much earlier leader, possibly one of the chieftans resisting the invasions of Julius Caesar or Claudius, rather than a late period Romano-Briton. If this was the case, and Arthur was finally defeated by the Romans, it would have been highly likely that his personal weapon would have been captured as a prize of war, perhaps even in a grand 'Triumph' through the center of Rome itself! If, however, the more likely historical explanation is true, then it is highly probable that any of the first three eventualities are in fact closest to the truth. Incidentally, it is possible that, if we ever do find Excalibur, we'll know it. Some warriors with "named blades" had the names of these weapons, or iconography indicitive of these names, engraved upon a portion of the weapon. There's at least a slight chance Arthur was just such the type to do that. So, here's hoping we'll find the sword you're looking for...

His sword was passed down from generation to generation in his family. It is currently being hiden from others outside the family in the USA.

According to the legend, it was returned to the Lady of the Lake, who would return it when it was needed again.

There's one that looks a lot like it stuck in a rock in Disneyland, Anaheim, California.

Scotland... or in your back yard??? who knows

I believe it was given back to the Lady of the Lake.

Interestingly, the legendary sword "Excalibur" or "Caledfwlch" seems to have been invented in the Middle Ages but based on a much earlier magic sword. This sword is described in the "Thirteen Treasures of the Island of Britain" or "Tri Thlws ar Ddeg Ynys Prydain", a mnemonic bardic verse of the type used by ancient Druids and Bards as an aid mémoire, initially recited and learned orally before finally being committed to paper of which some medieval copies survive. In this document, "Tri Thlws ar Ddeg Ynys Prydain", there is a magic sword; "Dyrnwyn, gleddyf Rhydderch Hael" meaning "White-Hilt, Sword of Rhydderch the Generous". This sword, it was said, was remarkable because if a well-born man drew it himself, it burst into flame from its hilt to its tip. If a low born man tried to use it it was useless. The owner, Rhydderch the Generous used to offer it to anyone, but they would reject it because of this peculiarity. This gave Rhydderch his reputation for generosity. Rhydderch Hael was a real king of the Welsh/British speaking kingdom of Strathclyde during the 6th Century AD. He lived in the period just after King Arthur. It is possible this sword, called "Dyrnwyn", is the same sword as that in the Arthurian legend, perhaps Arthur gave it to him? It is worthy of note that King Maelgwyn Hir, also known as "Maglocunos", the tyrannical "dragon of the island" and ruler of Britain in the late 6th Century is often considered a possible real version of Mordred, the legendary bastard son of King Arthur who ends up killing his father. It should be noted that Maegwyn Hir did, probably, kill his own uncle to gain the throne. His uncle was Owain Ddantgwyn meaning "Owen White-Tooth". Possibly this "White Tooth" is the name of the same sword which was later inherited by Rhydderch Hael? This is supposed because Maelgwyn Hir (Maglocunos/Mordred) had a war with the Britons of Strathclyde who came down to Gwynedd where Maelwyn lived and ravaged the place, possibly taking this sword away with them (presuming Maelgwyn who had stolen it from Owain Ddantgwyn). Later on this sword came into the hands of Rhydderch Hael, King of Strathclyde and was called "White Hilt". Some academics think this Owen Ddantgwyn could have been the real King Arthur because his true family name was Owain ab Yrth. This Owain also had the battle name "The Bear", which in Old Welsh is spelled "Arth" (his capital was at Din Arth). That would render his battle name Arthyr ab Yrth (Uther), Pen-Dragon of Britain, and his sword "White-Tooth". What became of the sword? The grave of Rhydderch Hael is believed to lie beneath a huge rock called "Clochoderick Rocking Stone" in Renfrewshire. Maybe the sword is here. The capital of Strathclyde was an impenetrable castle called Alt Clut on present day Dumbarton Rock. The king of the Britons of Dumbarton in about AD 570 was Rhydderch Hael, who features in Norse legends. It is said that during his reign Merlin stayed at Alt Clut. In 756 the first loss of Dumbarton Rock is recorded when a joint force of Picts and Northumbrian English captured Alt Clut after a siege, only to lose it again a few days later. In 870 the Vikings laid siege to Dumbarton for four months, eventually defeating the inhabitants when they cut off their water supply. The Norse king Olaf returned to the Viking city of Dublin in 871, with two hundred ships full of slaves and looted treasures. Maybe it is in Dublin somewhere, hidden and waiting to be found.