Came across another T-Shirt design space similar to Threadless and Designbyhumans - except this one made by an Australian crew, i do believe. 
Here’s what they said about themselves :

Wooshka is a continuous t-shirt design comp where you, the Wooshka community, get to submit design ideas, help decide which designs go to print as well voting on many other important decisions. Essentially, it’s your very own tee brand!

Every few weeks the latest winners are announced and their design will be printed and made available for purchase from the Wooshka online shop. Just 500 units of each shirt is printed to ensure the prints remain as limited edition.
The participants who submit the winning designs, as selected by Wooshka after score and comment review, will win cash and a Wooshka Gift Voucher when the design is first printed