So you're no longer a twentysomething nightclubber how do you meet single lesbians? If you live in a major city there are probably a few groups you can join and dinners to go to and (even in this day and age) the good ole lesbo potluck from time to time. What i'm thinking of now though, is that wider-choice, higher-risk option; the internet.
There are local and international paysites: qwomen, gwomen, Playdate etc. These cajole you in saying sign-up is free. It is, but you can't actually communicate with anyone unless you give them money. Fair enough, but what if you don't want to give them money? Does cheap/free mean you get a lower class dyke to date? Places like Gaydar give you limited interaction for free and hope you'll get hooked enough to pay. The trick there is to hand over an email address or instant message ID to whoever you want to talk to so you can chat elsewhere without being beeped at because you've just used up your free message allowance.
What can you get for free? There are old-school chat forums around, like QE2 and The Lounge, where you'll find a scene that appears dull on the outside, but gets incredibly lively behind the curtains once you're a regular and the old regulars feel reassured you're not a troll. There are also dynamic chat rooms at the two sites I mentioned.
Option three is, of course, Facebook. Clearly Facebook is despicable because it's big and bloated and everyone's using it and they're probably using our information to work out what tampons to sell us, but on the other hand, everyone's using it. There are a good few single S.A. Lesbian groups there, try plundering their member lists for new contacts. Then you can add new friends, send them stupid virtual gifts and take your time getting around to actually chatting directly. There are also applications you can use there to mate, er, flirt anonymously on and see if whoever you're interested in returns the interest.
The usual net caveats apply - meet in a group and/or public places, don't accept sweets from strangers, take a cattle-prod to ward off stalkers, blah blah blah.
Happy hunting.