Reputable pay sites where people post true profiles are actually your best and safest bet to find women seeking casual fun. You don't know what you're getting otherwise, and it's always good to have some honesty up front about what's going on, and to know who you're doing it with. Reputable interracial dating sites are prime for the women seeking casual fun type of relationship. So are some of the more famous hookup sites, like ashleymadison.com and sugardaddie.com.
Once you get on the pay sites, if you have a little bit more game, you can find women seeking casual fun on the free networking sites like Facebook. You must read between the lines here, however. Things like "spiritual but not religious" and "looking for adventure" combined with a single status signify women seeking casual fun.
After you comb the online dating sites and free networking profiles, you can top off your search with a trip to your local jaunts and haunts. However, make sure you are doing steps 1 and 2 so you can have your online mojo working while you go out. There's no guarantee you will be successful in finding women looking for casual fun just because you are. There's a whole nuther ballgame going on at bars and clubs. Suffice it to say you'll do better with a wingwoman. Good luck!