Are there any big campus events coming up? At my school, we have two big all-campus events, one per semester, and at the one in the spring, pretty much any organization can go and set up a booth for free. It draws a lot of attention from local businesses, who come to do contests and pass out free stuff. A couple new businesses did that at the last one, and now whenever I go, there's always students in there. Granted your campus is probably very different, but if there was someplace you could stand around on a busy day and hand out cheap stuff (cups, shirts, etc.), it might work. Or maybe send out flyers to whoever does the shirts at the various orgs advertising a contest, like whoever places an order will be put in a drawing for free/cheaper (insert product here).
When we pick who does t-shirts, we usually find a cute graphic in one of the many catalogs we get and go with whatever one it's in (unless they'll be outrageously expensive), so I think getting some samples of the work you can do, whether online or in a catalog, would definitely help. Anyhow, just my two cents.
