A made in America flintlock is the Thompson Center Hawkins or the Firestorm, also made by Thompson Center. Your last option is have a custom rifle made by an American Gun maker. Of course you will pay a little more for one of them then you would the Thompson Center.

You could check auction sites and look for a good used Thompson Center Hawkins or Renegade in flintlock. Sometimes they hit the boards and you can pick them up in excellent condition and save a few bucks.