There's nothing available that will be a complete "drop-in" replacement.
The trigger and trigger guard are one piece in that and a few other T/C models. T/C made their triggers 1/2" wide so that limits the choices to only T/C and direct T/C rpl triggers
(Investarms did too so they will fit the inlet but are a bit different).
The T/C double trigger will fit the inlet and function with the lock sear arm but it's shorter then the original (so there's about a 5/8" space left in the rear of the inlet) and the rear of the trigger plate needs to be inlet deeper for the trigger levers to reach.
Then you need the T/C double trigger guard installed as the TG actually serves to hold the front of the trigger plate in place. To do that the TG needs to be freshly inlet,, there are no existing inlets for the TG.
The composite stock of the Firestorm makes it near impossible, if you cut new inlets in the plastic,, there's nothing left to screw into,
:idunno:
The Firestorm is an interesting model being made to meet requirements for flint lock only hunting and to use pellet type powder charges, it's almost like a half-breed between traditional and modern with it's removable breech plug and still being a flint lock.