bagwell, I just bought a set of these aftermarket Carrera light rims from
www.wheeldynamics.com and the listing has the correct offset of 50 for the front and 47 for the rears... not easy to find, I assure you!
I paid $2150 including shipping for the four wheels and Michelin PS2's mounted and road-force balanced. I decided to buy my tires from him regardless of price because of the whole hassle factor of buying them elsewhere, plus the concerns about scratching the rims while putting on the tires. This way, the seller puts the tires on the rims and he has to insure they balance out right and don't get scratched or I get my money back.
BTW, welcome to the site. I live just south of you in the nicer part of Texas called Houston