I've run several outlaw paintball fields, and now an ACTUAL paintball field. One outlaw field was invite only. We had a website, and advertised our location with videos and posted on forums, talked to friends, etc. And it eventually built up. We had the original 20 guys playing there for about 3 years, didn't need any more than that.
You can try advertising on your local craigslist, looking for people to join you. This website, pbnation.com, etc.
Also, check for other outlaw fields in your area, do a google search and maybe invite them out.
Craigslist does bring out the douche-hats. So I would recommend having them send a little information about them. IE: How old they are, how long they have been playing, what kind of gear they own, etc. This will give you a rough idea of who you are dealing with.
Best of luck.