That's correct, the largest size TE37 SL's are 19". I'm eyeing those out myself. I don't think you need to go 10" diameter up front. 9.5" will do and it will still accommodate a 275 width tire. At stock height, you probably don't have to increase front negative camber to make the 275's fit, but increasing the negative camber will improve turn in response for sure. If you're slightly lowered, the 275's should fit with negative camber, but there may be rubbing at the fender liner at lock. Do you really need 275 at front though?
Check out ilive2win's threads:
New SL's....oh my!
ilive2win's 370z project
(post #277 and onward on the second link)