I wish I were working on a farm right about now, fo' shizzle!! I've been trying, for the past couple months, to seek out farms which actually have WORKING positions, but to very little avail. I'm kind of in the dilemma of not having a license (otherwise I would have bought a van a loonnngg time ago, and would live in that bitch!!), so the opportunities to actually truly WORK on a farm are far between. :\ I'm totally down with stealth camping and whatnot, butttttt as with most positions, I reckon they would like me to have a license and/or an actual residence.
Anyways. Regardless of all that, there is still hope.
I'd suggest you check out growfood.org, the WWOOF website, and/or pickingjobs.com... The first one, not too much actual feedback, but there are farms on there that actually have internships and/or stipends, and they all provide housing (of some sort). WWOOF - well, WWOOF is WWOOF, and you'd be hard-pressed to find any paid positions, unless you're damn lucky.
Pickingjobs.com - that one is rather interesting, and I've had a bit of luck with it thus far (but again, it always come back to my lack of housing/vehicle) :\ It just lists a bunch of farms all over the country (and world!!), and then you can email them and see if they need help. Best of luck!!