Use the usual sources like Ebay, Rennlist and Craigslist.
I purchased a few sets while trying to put together one set of 4, 16"x8" for all 4 corners on my turbo. I eventually purchased 12 wheels total

, 7 of which were 7" and the other 5 were 8"...kept the 8's and sold the 7's. I run the 8" on all four corners on my '86 turbo, 245/45/16, works well for rotating.
Just keep an eye on the classifieds in the above sites and you will find some.
Some of the wheels that I bought needed repair and refinish which I had done at US Wheel Repair in El Cajon.
