I believe that Peter Dyson (www.peterdyson.co.uk) may still have some original Damascus tube with which he can re-sleeve Damascus to Damascus.

The quality of his work is superb and priced accordingly so it would only be financially sound if the original gun is of very high quality.
You would also have to allow for considerable shipping costs to and from England.

There are others who can sleeve steel tubes into Damascus breech ends, and you may well be able to find someone to do this Stateside.