Have you seen WootStalker Tee Trade?
Since TeeTrade.org has been taken down, there was a void left for people wanting to swap their unwanted T-Shirts. I have made an addon for Woot Stalker that should provide much of the functionality. This is still pretty early production (as I only started on it yesterday), but so far it seems stable.
To add your shirt, log in, then click the "Add Shirt" link at the top. If you paste the original sale url into the top and click scan, it will autofill the info for you (except size).
Right now while in testing, only Shirt.woot is supported.
Please let me know if you have any questions or feedback.
*Note: Logging in automatically takes you to the main page. You can get to Tee Trade under the Tools Menu
Shirts listed by me are for testing, and not for trade
Thanks to @bluchez for all of the work that went into the original