Edit: Wait, I think I misread it originally, are you looking for a converter that needs to be modded to support expanded audio from the VRC6 chip?
Edit2: Either way, maybe this is the guy you should talk to. Seems he does a lot of mod work as well as stuff not listed on the post there: http://atariage.com/forums/topic/243676-modsrepair-service-now-accepting-orders/
Original: There's not really a lot of console modding people here, this isn't really an emulation-based video game community, so a recommendation is all that can be found.
Luckily for you, there's a lot of Famicom/NES converters these days that make that much easier than it used to be. I couldn't recommend one product over another as I don't have any converters for them myself, but this should get you started out on the right foot: https://www.google.com/search?q=Famicom+to+NES+converter&source=univ&tbm=shop&tbo=u&sa=X&ved=0ahUKEwijzvLxvJrbAhWk8oMKHewUCtYQsxgIKA&biw=1366&bih=634