For 17s, buy C5 Z06 Corvette front wheels. 17x9.5 and 19lbs.

For 18s, N73 option Magnesium Corvette rear wheels. $4000 option on '97-'03 Corvettes when new. Cheap when curbed or the paint is chipped.

18x9.5 and 19lbs. Ended up costing about $600/set buying 2 at a time.

The fronts are 17x8.5 and weigh ~16lbs. I have two for sale if you're interested. One is mint, the other is curb rashed pretty bad. $150 shipped for the pair of 17s.