This is a response for the group. First, what city are you nearby? We'll need to know so we can start providing names.
Second, a decent blackpowder gunbuilder can build a stock. However, (s)he'll need plans or dimensions so (s)he can duplicate the factory stock. It isn't hard or tedious but it does take skill & practice.
Vigilantibus et non dormientibus jura subveniunt. Molon Labe!