So far with those measurements, I can tell you what mainsprings will NOT work, due to too short of length from the pin to the end of the bottom leaf:
1. Original M1842 Musket
2. Repro M1842 Musket
3. Original M1816/22/40 Musket (BUT since these were NOT made on the interchangeable parts pattern, my two mainsprings may not reflect all of them)
4. Repro M1816 Musket
I am sorry, but it is too late and I am too tired to disassemble my "Recent Model" Pedersoli Bess, but I think the mainspring will be too short, as well, from the pin to the end of the bottom leaf.
I don't stock French Musket parts and MAYBE some of the repro's on the early models MIGHT be able to be fit.
With these measurements at the ready, I would first suggest you call Dixie Gun Works and see if they might have one or one that could be fitted.
These are two places in the UK who could make one for you:
https://www.blackleyandson.com/acatalog/Castings1.html
https://www.peterdyson.co.uk/acatalog/BROWN_BESS_MUSKET_Parts_and_accessories.html
If you want to stick with in the U.S., you might contact Earl Kathan:
http://www.flintlockrepair.com/
Hope this helps a little.
Gus