according to this article the M40 and M43 parts are identical and interchangeable.
Star Firearms : Firestar Series Pistols
to that end you might consider jumping on this auction quickly!Model 43 & 40
The model 43 and 40 are mechanically identical, and in fact almost all parts are interchangable. The only difference is in caliber.
Rare Star Firestar M43: firing pin + extractor : Small Pistol Parts at GunBroker.com