Years ago, before I found my current wife, I went through the same thing--tring to find someone who would give to me, or receive from me. I must have been very lucky, because I found a few "pro's" who were actually pretty nice folks. Apart from the money, of course. Such things can be quite expensive.
So here are a few tips: use the bdsm section of a site dedicated to advertising for escorts. You will find mostly Dommes, but occasionally you will find a sub or a switch. BE SURE they are 18+; most women begin to do this either because they don't want to have sex, and/or they are a bit "past their youth;" you will find a few that advertise for "medical play," or as "nurses." Many of the "nurse types" call themselves "head nurses." These are not what you want.
Call the girl. If it's a service, hang up. If she won't talk to you, hang up. Be specific about what you want. Tell her (no gory details) that you are looking for a girl who gives enemas, or alternatively, both gives and receives. Most Dommes won't receive. Alternatively, look for a girl who advertises prostate massage. She will probably have given at least a few Fleets. Tell her that's not what you want, that you want an old fashioned enema with the bag. You're buying her time, so she needs to know this will be an hour, though most girls I saw didn't really go by a timetable.
Listen carefully. If she says, "yeah, I can do that," she's probably not the girl you want. The girl you want will have at least some equipment, OR she will be inexperienced and willing to learn. but BRING YOUR OWN.
Remember, this is expensive. $300+ used to be about right, depending on the city. Don't ever use a credit card. Just cash. Be careful, too, since these girls, although they usually advertise "no sex," are right on the edge of legal/illegal.
And really, you'd be better off finding a loving permanent partner. That's the best.
As far as caring, most of these gals are actually not such bad folks. They are in an industry that is supposedly evil, but given the fact that they have chosen a path like this, you can expect them to be a bit hardened. If you are nice to them, though, they will usually be nice to you.
@SwitchableSusie is right, though. Other than a "pro," your chances of finding someone such as you describe are zero, and less than zero.