Well, I'm not going to sugar coat mine and Davids (NDN) situation. Even though we do go to a swingers club, he doesn't get to play as much as I'm sure he'd like. The main reason being that yes, single men in the lifestyle are a dime a dozen. The good thing however is that the more he's gone to the club, the more people have gotten to know him (and me). They know that we're a totally committed couple, that he knows how the lifestyle works, and that he can be trusted to play with other mens wives without crossing any lines. He's also had the chance to play with a few single women after they were assured (by me directly) that I was ok with it. We've even been invited and gone to a few house parties by other club members that we've become friends with.
MN Tom is right. If you choose to make a profile on a swingers site, it will take some work. You'll need to be creative to catch the attention of couples or singles looking for a single male to play with, and yes, you'll definitely want a way to verify that you're married with permission. With David and me that's easy, as I go to the club with him most of the time (as of right now that's the only place I feel comfortable with him playing aside from the house parties we went to). Taking your wife along for the first meeting is always a good idea. That way she can be there in person to give her permission, and any rules, boundaries, concerns, etc. can be laid on the table to be discussed.
Just don't get discouraged. It's true, couples and single women have a lot more opportunities in the lifestyle, but there's a place for single (or in your case, married with a hall pass) men too. You just have to work a bit harder to find it.