GSG Firefly trigger wont engage hammer.

[Joelski]

For this one I would look for someone that has a Sig certification. As far as I know the GSG is the same as the previous Sig Mosquito.

^^ This. A certified armorer should be able to quickly diagnose what's wrong and effect quick repair. Ask at your local gun store; most good repairmen have good word of mouth endorsement. The same can be said for not-so-great gunsmiths.

Good luck!