I have bought from this Ebay seller (not affiliated, btw) and I think she has great prices. I see right now she just has one size, but she usually has more. She also carries the clear plastic boxes for making card sets. I would do a search on Ebay, there are many sellers, and most have very reasonable prices and good variety. HTH!
http://search.ebay.com/_W0QQfgtpZ1QQ...3aMEFSQ3aMESOI