There aren't many shops in the bay that works on GTRs. The market is no where near as big as socal. I think a lot of owners here drive down to Socal to tune their cars.
Z car garage works on Nissans but they are pretty expensive.
ask biznaka about Cobb. He just took his car down their for a tune and install.
There are shops that can work on GTRs but most places around here can't do a custom tune if that's what you're looking for.
SonicMS can do switzer packages and carry a lot of exhausts and wheels for GTRs.