Remember that most groups that are child free are that way naturally so you don't have to seek out "child free" groups at all. For example I'm a wine writer and I go to a lot of wine events. There are NEVER children there and there is pretty much never discussion of children either. The discussion is all about wine.
I belong to the local chamber of commerce which is for men and women in business. Many of us members own our own businesses. When we have our get-togethers the discussions is always about business, about networking, about what we are doing in our business. again, children pretty much never come up.
So don't restrict yourself to a group about "not having kids". You might not have anything at all in common with those people except that one fact! Instead, if you find a group that revolves around an adult hobby it will naturally bring in people who share your hobby interests and who will be talking about that hobby. Probably the only exception is if the hobby is something like "knitting baby clothes"
