When it comes to domination, you get what you pay for... and sometimes you don't even get that!
If you're looking for something more lasting than a single session, check out fetlife, and get involved in your community. It can take time, but getting involved with actual people and building a relationship does indeedy take time.
If you want something quick and dirty, you can take your chances with online posts and forums, and you might hit paydirt, even!
Or you can look for a professional with a reputation, either a dominatrix at a dungeon or someone who works over the 'net. If you go pro, you're gonna lay down some money, but with someone with a reputation and presence to defend, you're more likely to get what you're looking for instead of just taken for a ride.
Good luck!