Another vote here for finding expired film. It crops up on eBay with some regularity, although eBay isn't flooded with the stuff. FWIW, I bought some expired (1989 and 1992) Svema color slide and negative film a while back. I've got some of the results posted
on my Flickr page. Most of the posts there are from the slide film, but I've got a couple of print film shots early (on the second Flickr page).
Of course, if the film is too old or too exotic (like my Svema), you'll have a hard time with processing. I do my own processing and am comfortable mixing my own developers, so I managed to do the job with my Svema, albeit with some fudging on a few details. Formulas for C-22 (used for Kodak color print film prior to the 1970s) are readily available, should you get something that old. Most color print films sold in the US since sometime in the mid-to-late 1970s is C-41, which is the current process, so developing it shouldn't be a problem.