This whole situation is going to be weird. My advice is to stay away from Craig's list and similar for a few reasons, go a more trusted route.
A) Safety! Not only the ladies' safety, but yours. First of all, are you going to get these girls blood tested? While there's no want for blood, that's not to say that an errant slap or a wrong fall wouldn't produce a cut or scrape. What do you do when one of those women has a disease (from the avenue you're pursuing you might get women who might be on something or living a rough life). Then you've just possibly contaminated someone else or yourself. So you're liable. Or!
You find these women and you're all over it. You tell them to come over. Only to find that one's really a guy and you get yourself robbed for the money or the other lady begins getting stalked. Maybe it's the job I work, but there are creepy people out there. And ask any session girl, there's a lot in our corner of the world.
B) You may hit gold and find women you find attractive. But if you're only offering money to the winner, you're bound to attract women who are hard up for money and more willing to hurt/break the rules more.
C) Insurance. You're asking these ladies to do something that can hurt them. If they work, how are they going to get money to cover being off for a few weeks with a broken foot or something?
D) Legality. Is it legal? What is the legality of getting two women to catfight each other? You should look into that. Because being arrested over this wouldn't be a good thing.
My advice is to research and save money. Once you cover your bases and get money saved up, avoid craigs list and post in a news paper, at the gym, on a local college campus, look at WB270.com. Somewhere where you won't get in trouble, but somewhere where you'll attract people who might be shady. You'd be amazed at where a woman might see it and say 'that sounds like fun.' It's all in how you word it. But pay like $500 to both for the hour and then surprise them with a bonus at the end.
I always see these posts about paying hookers to fight and to me it seems really messed up. These are human beings. We're not free to treat them how we want for the purpose of our 'fetish.' Instead, we should look for those who want to be involved. In fact, you may even know a few girls who'd do this for you for free. Back in my wild days, I had a few girls that were interested in the world of female wrestling/catfighting and might have followed through if I asked them.
If my suggestions don't sound fun (remember, this is real life and one big screw up can ruin that one real life), then look at producers who let people go watch their videos be made. I know Renee used to let spectators come watch. Look around. It may be less hassle and easier/quicker.