I think Reading will be having one sometime in October or November and there used to be some in Maine called York Powder Burner, but I think that is over. There is a big supplier of BP in Maine and they used to sell st matches, try giving them a call see if they can help you.
A bunch of BP shooters get together on Tuesday morning at Reading.
Pembroke used to have a Turkey shoot by the cabin. Not sure if that is still a thing.