There are actors' sites, and there is Craigslist, where you can look for and find actors.
You can find actors willing to work for no pay, just for the experience and the footage for their reel (please be sure you get them their footage, if it is something you offer as compensation), but I can tell you that you will increase the number and level of actors applying if you offer a small daily stipend - $50 a day will get you an exponentially better quality of performer.
I, personally, do not submit for any non-paying roles anymore. I will work for friends who have projects who approach me, but if an ad on L.A. Casting or Actor's Access says unpaid, I click past it. It's probably partially an ego thing, but at some point while I was starting in stand-up comedy, I had to say, "I'm not doing any more unpaid gigs, unless I'm testing material for something specific - unless I benefit from it." Same with acting - at some point, you have to make yourself a professional to separate yourself from the amateurs.
gelder