I'd give Dixie Gunworks a try, they did have quite a collection of original parts. You might also check S&S, and Romano Rifles to see if they by chance have a lock. Centerfire breechblocks are available from several suppliers, Dixie, Buffalo Arms, S&S, etc.
Whether or not the Armi Sport parts will fit, I do not know. At the least, you could try them and if they did not fit, maybe they will let you return them-- that I would find out in advance.