Use Your Gamer Launch Account
Your account from any Gamer Launch site is valid here.
If you already have a Gamer Launch account connect your Facebook account on your user profile first before using Facebook connect to login. Otherwise you may end up with a new account.
There is a link in the OP as to how to buy a Wook shirt. From that link you can select color, type, and there's also an option to add a custom name on the back.
There are two Pink color options; you can check out all available color options here: