I just wanted to share some resources/ideas that I have found to be good for finding more atheist friends. I have only been an atheist for about a year now and certainly need more atheist friends.
The best way I have found so far is to go to meetup.com (will help you find friends IRL) and search for local groups by using the keywords: atheist, freethinkers, free thought groups, secular humanists, even some unitarian groups are ok, recovering from religion groups, science fiction clubs, philosophy clubs and really any other subject you may have a personal interest in that is likely to have atheist-minded people forming groups where you can find as many friends as you personally feel comfortable with.
Anyway, we don't have to be alone or lonely, there are people closer by than we may think to be friends with. The real key to getting more friends is to actively seek them out. Good luck and I think you will find success if you really want new friends.
If you have any ideas or resources that I left out, please share them so we can all benefit together as fellow travelers on this road called life. Take care everyone. :)