I've found a company that makes custom T-shirts here in Pondicherry, India. They also ship stuff to France regularly. If there is enough interest I think I can get some GNUstep T-shirts printed for FOSDEM (50 minimum). Checkout their website http://pondylifestyle.com/
Pricing is around 6-7 USD.
Cheers, -Krishna
-- Why make things difficult, when it is possible to make them cryptic and totally illogical, with just a little bit more effort? - Aksel Peter Jorgensen