I *used to* consider myself "childless not by choice," now I consider myself childfree as I CHOSE not to have ICSI (IVF). DH & I chose not to adopt as well.
It took lots of some time, effort and support to find peace in all of this. I found that being with other women in my boat helped me on the journey to acceptance... and eventually... (dare I say it) gratefulness for who I am. I am a woman and I do not have kids. ( A rarity in our child-filled culture.) I found this unique type of support on a couple of web-sites (listed below). I ended up meeting some of these women in person also.
Anyhow, Childless1, I think it's great you are looking to find support & friendship with others who "get it." You are among a unique group --- you are right, it's tough to fit in with groups who are "militantly" against children. Though you may find comfort in having friends from those groups (people who also don't have kids), you may not find others who understand your feelings of loss & grief about not having children. It's definitely a grieving process. Peace in this issue doesn't happen overnight, but it CAN happen if you seek it!
Here are those support sites I mentioned for Childfree / childless women (not by choice).
www.lifecanbefull.com (The focus here is living life to the fullest.)
www.childlessnotbychoice.com (This site is Evangelical Christian in nature, but there's wonderful support if you can fit with their beliefs.)
The INCIID site (infertility) has some chat boards, here is one for exploring childfree (after infertility)
http://www.inciid.org/forums/exploringchildfree/index.htmlI found that my RESOLVE group was sorely lacking in support for those who "choose" to "resolve" their infertility by remaining childfree. It was excellent support, though, while we were figuring out what to do.