Cheating is more culturally acceptable. Unfortunately that is the way it is as far as I can see. Its more of a threat to know that the wife is okay and that everything is above board than to sneak around behind peoples back. It can also be threatening to think that it might last longer than a quick fuck and that there might some expectation of committing to something more.
If I were in your situation I think I would not think of this in the same realm as people who are cheating and especially not in the realm of your colleagues who are cheating. If your wife is okay with you having a gf or even the occasional "open marriage" fling, then that is completely different than cheating and should be treated as such. You can be confident in that, stand tall, go about finding a gf from a place of integrity, honesty, respecting those you love and the women that you are interested in. Market yourself that way because that is something to be proud of. Sure, you likely will get some that frown on that, but whatever, they are just ignorant and undereducated. I would do my best to educate them and if their remarks continue then they are likely jealous that you have it so good.
Maybe try looking for local poly groups, go to dating sites that you know are poly friendly such as OKC and start a profile that mentions what you are looking for. Invite women out that you know are single and start talking poly up to them and those around you openly. Chances are there will be some interest eventually. Things that matter take time, affairs take less time because they don't matter.
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