In a link from the comments of this article I found another article about a company's t-shirt development process: http://www.myintervals.com/blog/2011/02/01

In a link from the comments of this article I found another article about a company's t-shirt development process: http://www.myintervals.com/blog/2011/02/01/submersible-dirigible-the-new-intervals-shirt-design/ Of most interest was their response when someone in the comments asked for a t-shirt: "Yes, we are giving them away. Login to your [...] account and click on the feature request button at the bottom of the page." Seems like a good approach.