I think that the Basque guns have been around long enough that most gunsmiths with good reputations are capable of doing the work. Much depends upon personal preferences for this kind of thing.
For example, Nick Makinson will be more than able to do the work but he is a firm believer in making sure the entire system of the gun is working well. On these guns, Nick is of the opinion that a sticking ejector may be more of a symptom than just an isolated incident. So far, I've done it both ways and I'd have to say Nick has been right.
So, depends on how much you want to spend and how long you are prepared to be without the gun.
NECG would also get my nod as would Del Whitman for what is essentially a metal issue.
Otherwise, I'm hearing too many stories of smiths going to semi-retirement or having large backlogs to give a host of names.
