First, it appears such a site already exists -
http://www.cafepress.com/tclug (linked from mn-linux.org)

Second, the big issue Ubuntu LoCos have run into is that most groups
are not legal entities (and it rarely makes sense to become one), so
there isn't anything to actually give money TO.  This means that
legally speaking, no matter how you slice it it will just be some
individual holding onto the money anyway, so it probably makes sense
to have that person be the one who is involved enough to put in the
effort to make the stuff.  If they want to then spend it in some other
way that benefits the group, great, but there isn't really a way to
make that have to be the case.

 - Tony