So are you willing to put aside some "expenses" for your encounter with these gaijin hunters? Because a gaijin hunter you'll bump into in Roppongi is most likely interested in your wallet than you. They may be freestyle escorts or girls who work at bars who are looking for potential customers to go back with them. If you have an entertainment budget, then it may not be a problem. Just be careful, do not step into any Venue without a legit website.
Girls who are working for bars / clubs may be straightforward and give you a card of their club. You can check the website and prices. Some girls don't tell men where they work and they just drag guys into clubs and I think that's bad image for the working girls. If you're looking for freestyle escorts, you may check out r2.