Edit...just reread your post.
Are you wanting the stock Camaro pattern, with just your own material? Or you want the pattern to match the front seats?
http://www.tmiproducts.com/ They can take your fabric and make you a rear seat cover. However the pattern would be stock Camaro. But for example, the insert part of the seat could be changed to your material. I'd give them a call and chat with them...it would be cheaper than $600.