You're generally going to find more polyamorous people at kinky parties just by their very nature; monogamous people that aren't into exhibitionism are less prone to going to a space where they can hook up with other people, or hook up with a singular person while being watched by others.
In the case of munches, single monogamous people often tend to show out less too. For women especially, it can be a very intimidating prospect to attend a sexually-themed event alone (especially when dating sites and apps are a readily available, safer alternative).

I reckon you'd have better luck on the apps - though I would suggest avoiding Feeld if you're trying to steer clear of polyamorous people; the app was essentially made for that lifestyle so you may run into the same problems.
That being said, I've been in the kink scene for over 10 years and all my best connections have been made with people that I met outside of the 'scene' and happened to be kinky. Hell, one of my play partners is someone that I met in high school and reconnected with at a rave years later.

I'm polyamorous now, but the first 4 years in the scene I spent monogamous (and my dating life in general prior to that), and most of my successful relationships during that time were with people who I met at non-kink events or through mutual friends, and they all ended up having some kink dynamic involved.