Mate Toymods Car Club members can buy extra shirts so if you want a smaller shirt and a larger one as well then just pay the normal joining fee and then the normal amount for a new shirt.
I can't say I can remember how much that is but Stitt will be able to help you out. He has a thread at the top of this forum section with info on joining. I think he is away for a couple of weeks at the moment but he'll sort you out when he can.