Actually, Dixie just might be able to help you. Years ago, I bought a Pedersoli Kentucky that Bubba had "improved" by trying to change the trigger action by filing the sear and tumbler. It took a while, but I found out that lock internal parts for Dixie's Deluxe Cub,Super Cub and Pennsylvania rifles were drop-in replacements for the Pedersoli lock. I bought a sear, tumbler and mainspring and they went right on that lock.
And I do realize that you have a flinter while my needs were percussion, but Dixie still sells a flintlock upgrade kit, replacing flintlock internals with percussion-style parts (tumbler with stirrup, appropriate mainspring, etc). Seems like many dimensions are similar between flint and percussion.
Anyway, if you want to check it out, the frizzen part # is FP1401 ($22.50); the frizzen spring is TP1402($7.50). It just might be worth looking into. Anyone else ever try this?
Something to think about. Hope this helps.
sneezy