Originally Posted by james Haury
you might be able to convert to a modern 3 pc bb . Check with Sheldon Brown give him a tinkle on the telly ,9a to 5p eastern.
If its a Thompson, his likely answer will be along the basic lines of "we don't stock any parts for that" and/or "best not to bother with it"
But I don't want to speak for the man, he's around here somewhere, no?