None of us have Sigs, but awhile back some guy was selling a sig 556 on craigslist in modesto for 120. I dont see his listing anymore, but i do have his phone number. maybe the parts are compatible. 1209-552-9191
I dont know his nam, but i was texting with him awhile back.
Also I just remembered a guy that sold me my mp40 had a sig 552 for sale. He wanted 70. He's in sac, I forgot his name, most likely he will still have it. 916-317-2526