I agree with Merlin. If swinging is an important part of your life and you'd have problems being within a relationship with someone who didn't like the idea - then best you don't get in a relationship with such a person in the first place.
As part of your flirting behaviour you need to make people aware that you are someone who's sexually experimental - that way you will frighten away those who aren't cool about it and attract those who are both interested in it and in having a relationship with you. Obviously you need to do this in a sexually attractive way - if you just blurt it out then you'll frighten off everyone!
If you don't make it clear from the start you are likely to cause a lot of problems for yourself. It's easier to start relationships with people who are already in to sexual experimentation than to 'convert' someone who thinks it's weird.
I have often been surprised by how many people will admit to having tried, or who want to try, mild BDSM, bisexual experimentation and threesomes and will admit to it in a flirting type situation. I'm sure the same holds true for swinging.