The last documented date I could find on Excalibur was a brief mention that on March 7, 1193, King Richard reportedly gifted the sword to King Tacred of Lecce. This was part of a peace negotiation between the two Kings. Tancred had kidnapped Richard's sister, Joanna, when her husband died and Tancred assumed the throne.
This rumor actually caused a major uproar amongst the lesser classes, who had heard of the legends and myths (born anew through the courtly love poets).
Please note, the controversy was unnecessary. The gift was part of a dowry that would to go Lecce's daughter, who was betrothed to Richard's 4-year old nephew, Arthur of Brittany. Since Richard didn't have any children at the time of negotiations, he planned to make Arthur his heir and the dowry would be returned to Briton at the time of their marriage.
In short, it was supposed to be a "temporary gift."
However, King Tancred died in 1194, and his son, William III, was dethroned by Henry VI von Hohenstaufen of Germany. Whether the sword actually made it there, no one knows.