I've never seen a large hit'n miss model capable of doing real work. speculating here, but to do real work it would be too large for home shop equipment hence there'd not be much of a market. how many hp are you looking for, what work do you intend it to do? I'm making one myself, so get the allure of them, but I'd just use a modern efficient (comparably) gas or eclectic motor to do work.
have you considered restoring a real one if you want a larger size?