It's tough out there. My best advice is to date people in nurturing/caring type careers. You don't have to resort to fetlife or alt.com.
The relationship won't last if there is just a sinuglar compatability.
If you a male you are going to have a very rough time. I won't sugar coat it. Male AB's compete for a very limited population of female playmates. So you will often be competing against men with power careers, high education levels, good looks, and serious financial resources. That doesn't mean you can't land a mommy or daddy. It just means you will have to market yourself better.
If you are female, it's easier, but as my wife will attest you end up dating a lot of toads and pervs. Plus, you will be competing against all the younger women and that gets tiresome fast. It is also exhausting to get your hopes up and have them smashed to pieces when you find out they aren't daddy's but ABDL guys who try to bait and switch.
The biggest mistake people make (besides lying) is being 1 dimensional. You are more than just an AB. After the play is over would the other person want to hang out with you and do other fun stuff? Basically, are you datable outside the abdl realm?
Now to the IRE of many females, I will tell you that the mommy's age can play a factor. Women in "Get Married" and "Baby fever" mode (25-33 years old) will be the most likely to overlook and accept your fetish... IF the rest of the package is there. You pretty much need to be solid boyfriend material in all other respects.
As a daddy one of the things I always sought out was someone who could be a complete and independent adult when appropriate. Can that person also be at least an equal partner? Do I have to support them or can they make it on their own? Can I see her as more than an adult baby?
It would be great if there was an easy way but there is not.
If you do go alt.com or fetlife, do yourself a favor and know what you are looking for. Also have great photos on the profile and make them recent. They don't need to be ab pics either. Do yourself a favor on your profile and don't be too demanding or make it all about you. Talk about what you are willing to give in a relationship. Huge plus points for that. Discuss what you do for a living, hobbies and interests besides the ABDL realm. Remember complete package.
Also when contacting people remember they get hit with 100 perv emails a day. In your messages be polite and don't let baby talk or phrases like "r u wearing" or "do u like diapers" get sent.
If you don't know how to flirt read up on it. You will need to be able to woo the woman or man, not just the mommy or daddy role.
If you don't feel like competing or investing in a relationship, then hire a professional to satisfy your adult baby needs.
I know it's rough but hang in there. All the hard work is worth it.