Amen, Susie! We were very active swingers from the mid to late 70s until the early to mid 90s. We enjoyed every minute of it and made a few long lasting friendships that still exist today even though we haven't had sex with any of them in years.
We met other swingers by going to swing club parties and never mentioned our swinging to our other friends or relatives. I wholeheartedly agree with Susie, it would not be a good idea to mention this to friends unless you are sure they might be receptive to the idea. Even if they are, once you swim in that pool the dynamics of your friendship will be permanently altered. I would leave my outside friendships alone and make new acquaintances within the swinging community. Most all cities have swing clubs and they can easily be found on the Internet. Most swingers are responsible, polite people who respect the word, "no". The first club we joined offered an informational Q&A session at a restaurant for all those who were considering joining. This was a great idea, they explain the rules and what is and isn't acceptable behavior.
Some other points: before you do this, be sure of the strength of your relationship. Don't do it to spice up your marriage. If the sparks no longer fly between you and your spouse or if you have other problems, swinging won't help and will probably have the opposite effect.
If your'e ok with all this and decide to try it, give it a chance to succeed. My wife came home in tears from the first party we went to because none of the people there appealed to us. The second time we went we met a group of three couples we were instantly attracted to. They took us under their wing and we all became fast friends and met several other couples through them.
One last point: It's usually the men who bring up the idea but the women who actually become more enthusiastic as time goes on.Good Luck!