i don't know of any off the top of my head but VersionTracker (http://www.versiontracker.com/) has an "Advanced Search Option". If you checked off all the software categories, picked only Mac OS software (not Mac OS X or Mac OS and Mac OS X) and used "68k" as your only keyword, I imagine you'd get a long list of mostly 68k compatible software.
you might also want to try the info-mac hyperarchive at MIT. they've got a lot of old shareware, freeware, etc that is 68k. (http://hyperarchive.lcs.mit.edu/HyperArchive.html)