Are there any sites where I can find people for a 0 budget collab?
I guess a standard place would be the Help Wanted section of the gamedev.net forums. Really though, you need to get creative, set yourself apart from the crowd. Do you have a prototype of the game made yet? If not, that's something to consider - having something actually functional to show is leagues ahead of some guy with some game idea looking for employees that work for free.
You could also look around for any communities focused on game development in the particular genre of game you're looking to make. For example, if you want to make a roguelike, there are tons of communities just about roguelikes. If you want to make a generic RPG, maybe not so much, but a steampunk RPG, there's bound to be some steampunk RPG development communities out there.
Networking is important too. Maybe look around on Twitter or Facebook or LinkedIn or career sites for game developers looking for jobs. It's a stretch, but you might get really lucky (especially with a really good idea) and convince them to work for free.
It all comes down to the quality of your idea though. What's in it for them? Not money, so you better have a darn good game idea to compensate.
Given that you just need art for a finished game, you might try art-specific forums as suggested in the comments. You might also try looking around someplace like deviantART for someone with the art style you're looking for, and then send them a message. I can't say it's the right approach, I have no experience to back it up, but I feel like being more personal (as opposed to sticking a post in a forum) would help increase your chances of finding a good artist who will work with you.
The Help Wanted forum of Gamedev.net can be quite active with projects, both finding talent and projects to work on.
Ricket gave some solid advice above, but you might want to add the TIGSource Forums' Unpaid Collaborations to your list of places to investigate. They have a pretty active community of 0-budget developers and artists. Also, if you're willing to use pre-made art assets/sound/music, you should check out the results from their Assemblee Competition.