You may have some luck on Reddit's /r/freelance.

Another idea would be to hit local meetups for the web industry and talk to the people there. You'll get a sense for who's busy, and who you might be a good fit with.

Also, look at industry publications and see who's writing for them. These are typically very bright, very busy people. Try to become useful to them and you could end up getting an excellent education under their care.

The key is to remember that busy freelancers are always worried about wasting time, so you have to overcome the initial fear that it'll take longer to show you how to do something than for them to just do it themselves (and the subsequent fear that you won't stick around long enough to recoup the training costs). If you can empathize with that and come up with solutions and systems to PROVE that you will save them time, you'll get a lot further.

Good luck!