Dagnabbit, I wrote a reply and must not have hit "post".
Some of the Lott locks can be fitted with parts from some of the Brown Bess repros. That isn't going to help much from a cost perspective, as the cost for parts is about the same--but it is something to keep in mind if you need a new frizzen, tumbler, etc.
Making a sear spring isn't much of a problem . . . if you know how to make springs. Bending one up out of an old spring (looks like this is what Ohio Joe did) is probably not going to last. If you want one that will last, it will probably be best to shape etc, temper, then fit it to the lock.