The Rifle Shoppe has many different snaphaunce and miquelet sets of lock castings. I just received a snaphaunce carbine lock set from them this week. They make a lot of their parts after they take orders, so the wait time can be almost infinite. I asked if they had all of the parts for the lock that I wanted in stock, and they said they did and that they would ship them out the next day. It took about 2 weeks before they shipped though. This is very typical for them. Figure that it will take at least 3 times as long as they say or more.
In most cases, the wait is worth it. It's just best to only order if they have all the parts in stock. For some reason, their website is down right now. They've been saying for a long time that they are planning on revamping their web site. Maybe that's what they are doing. Their phone number is 405-396-2583.
Blackley & Sons, which are located in England also sell several lock sets including a snaphaunce lock set. Their quality and service is phenomenal. Right now the exchange rate is prohibitive for U.S. customers though.
I have a book by Robert Held, "The Age of Firearms: A Pictorial History" that has a diagram of the internals and externals of a snaphaunce lock as well as a lot of other types of locks. If you are interested, you can send me a private message and I can snap a picture and send it to you.
Building these things tends to be addictive. Once you start, you'll want to do more. Welcome to the club. Let us know how it goes.