This is an interesting thread, and it probably depends on what you are looking for....
A long term relationship is far and away the hardest, no matter what your "kink," just like it takes some time to form a really meaningful relationship. In my dating days I would eventually tell my partner about my kink (enemas). I've never had anyone go running and screaming away, even if they weren't interested. On the other hand, come on too strong.... they're gone. I guess my best was when I told the woman I was seeing, she took it all in, and the conversation turned to other things, now keep in mind we already had a nice relationship building. A few nights later she tells me she had gone to her mom's place when her mom was at work and tried an enema. She said it wasn't bad, but it didn't do anything for her, so I let the subject drop. A few nights later while we were making love she asked me to give her an enema.... If I had pushed, I think things might have been very different, getting too over the top with you partner is likely to spoil a good thing. That enema had her cuming and cuming, and was the first of many!
Now a few years ago, when I decided to partner with Anika Sondholm and make some enema videos I wondered where we would find models willing to do it on Camera. I found a first class on-line service that had a number of models available. I contacted one of the most beautiful women on the site, expecting a resounding "No!" What I got was I'd like to try that, and from there out about 1/4 of the models we contacted were willing. One model was already into enemas and colonics.. and a looker, too.
So what's my point? We decided to go to Backpage.com and see how many that advertise there would be willing, turns out about 2 in 10 would be on the receiving end, Some wanted an additional "tip." None of them were unreasonable. What we did find is that a lot of these ladies are looking for steady, repeat customers. Be careful, some of the ones that claim to be just 18, with reference to being very young are sting operations run by the local cops... we just had a news story about that. Usually the ones in their 30's or older are a safe bet, and we know one single mom, about 35, really into it.
We also tried advertising on Craigslist for a woman willing to give enemas, no mention of the sexual side, and we got several responses, including one 28 year old who turned into a willing playmate... Plus a number of caring, gentle enemas from several others.
So there are options....