There does not seem to be any open source C emulators for the 2600, only ASM ones, making it a bit hard to port one.
I have been working on a BBC Micro emu (people in the UK will know

but have been a bit busy lately and have not been able to do as much as i hoped.
If someone wants a good 'first emulator' project for the GP32, try the CHIP8, it has to be the most simple machine to emulate ever, I had it running on my gp32 within an hour.
-Craig.