Well, I don't exactly know how to go about getting a mommy, because I've never had one. But I assume you'd need to develop a strong friendship with a female and "come out of the closet to her" and hope for a miracle, that she'll want to be your mommy. It's pretty rare.
And then of course, I think you can like, hire a mommy off some websites. You have to pay for her, though. But, if you ask me, it wouldn't be the same.
There are women into the caring/dominating side, who may not be infantilists per se but are willing to adapt their needs to yours. I have known a couple who get the concept though did not actually form such a partnership. That said, this is absolutely not the place to find a mommy. This is a great place to find fellow anime enthusiasts; not so much for women wanting to join in live role-playing games. I would add that compatible personalities should be the first priority, not compatible fetishes.