where to buy booty shorts?

These are popular
http://store.americanapparel.net/7301.html?cid=178
Here is a good wholesaler, You will need some credentials to set up an account, or work with your printer, if they are worth there salt they should be set up to order for you.
http://www.tscapparel.com/product/0436am/girly-running-short.html