Yeah, I know exactly what you mean, especially if you're Glasgow based.
For practical purposes, I'm restricted to 8-10 AW girls in Glasgow and half a dozen Edinburgh sauna girls. (If I'm going all the way to Edinburgh, I don't want to risk an AW punt when I can usually book a reliable one in the saunas.) However, the market is shrinking, as you say, and so I may go for Edinburgh AW after the festivals.
The best way is to spread your bets; be prepared to go the extra mile (literally). Having said that, I'm still not so desperate for better choice/value that I'll go to the agencies. Paying well over the odds for an unreliable punt, a lot of which goes straight into a pimp's pocket, is not something I'm (yet) attracted to.
An almost forensic study of this forum will also help, which I admittedly don't do as assiduously as I should.
It also depends on your "type". Sometimes you may have to take a risk (financially I mean, not physically or legally) if a WG's your type but, again, that's a counsel of perfection because I don't do it very often.
Personally, I've got round it by visiting a relatively small number of girls relatively often each. But, if you're a "never go back" guy, that won't work.
More questions than answers here-would be good to hear from others.