Well, the Fraser seems pretty simple to me (but I couldn't machine a toothpick). It is strong and smooth to operate (the one or two that I have handled).
Steve Earl may have plans he would be willing to sell someone for a one-off project. No harm in asking anyway.
English singles are pretty elegant, but I think it is one area where the American actions hold their own, maybe even with a margin to spare. If Winchester Singleshots weren't so dirt common, they would have become the most prized singleshot of all time. In my opinion of course
Brent