Here are some on ebay. Also check craigslist, so they show up now and then. Be careful, lot of people sell Camaro wheels as 71-72 SS wheels, they are different. The Chevelle wheel has a rounded spoke, the Camaro wheel has a flatter spoke. They are pretty similar so you could get away with using the Camaro wheels unless you really want it to be correct.
http://cgi.ebay.com/ebaymotors/cheve...item20b1e58a55