Where can i get my new rims and tires put on my corvette?

[Arrowheadfan]

I have a c4 corvette and the tires on the origanal car are 275/40 17 and i bought new rims, and the new rims in the back are 295/35 18 and every place i call they say they can't put on different size tires, its not alloud. I call wal-mart for this. Les shwab cost over a $100 just to change the tires and balance them