From what I've seen, most ABDL company ambassadors are chosen due to their follower count on Tumblr blogs or other social media presence. So, first you need an ABDL blog with great content, which will attract followers, then with followers (and lots of activity/comments/likes), the ABDL companies will come to you.
This isn't spreading awareness of ABDL to anyone who's not already aware of it though - I'm not exactly sure if most ABDL companies really WANT to be known to the general public, it could cause quite the stir. That would be up to them to decide though, there's a few that read these forums.