Instructables has instructions on how to make a tape cassette that loops.
6 second cassette tape loop instructionsLooks like it might work!
I just dusted off an old tapedeck I was going to sell and decided against it (since it didn’t look like it’d make more than 10 bucks or something) so I will try to find some time to make one of these cassette loops.
If you are willing to risk some damage to the deck, check out
http://www.f7sound.com/tapebreak.htm
I think cd-players aren’t so picky so http://www.f7sound.com/cdscratch.htm might be fun aswell.
Thanks for the links, will check it out. And hopefully I’ll have some time this weekend to create some 6 second loop tape cassettes with some of my loops.