Here is the seller I got them from:
http://www.ebay.com/itm/400664120627?_t ... EBIDX%3AIT . They are pretty cheap, They have them cheaper than the company that makes them. They auctions for 25, 50 or 100 counts, and you can buy more than one set. I don't know these people, but was very happy with the sell. They seem perfect for shipping or storage of extra box's. I wouldn't advise putting in bad condition box's, as pulling them out might be a little hard, or damage them.
I inserted these box's and pulled them out with no problem several time's.
Tony