Although you can see that I have a lot of reviews on kgirls, I actually see a variety of ladies of various ethnicities. I have a few girls in my rotation that are UTR, who are black, caucasian, hispanic, mixed ethnicities. I've found a couple of gals that are ex-porn who have retired but now work as providers. I can't review most of these ladies because they don't advertise, and/or want to remain UTR and can only be reached via introductions. I personally love the variety that can be found in LA. I love a hot sista!
But it is a buyer's market. The $250 rate is very attractive and if one is a kgirl afficionado it's hard to deny the convenience, relative safety, incredible service, and easy booking that the agencies provide. So it's difficult to compete with that particular client base in LA. There are also other avenues outside of Cityvibe, another very popular "social networking" site that has a relatively small Asian footprint, and the price point is in the $250 range. So you may want to consider the competitive rates that are dominant in this market.
So IMHO there is PLENTY of room for providers of all ethnic persuasions, I think the LA TER and CV scene is just a small piece of the pie when it comes to the hobby, and you can't judge by the lack of reviews on TER of African American providers as a true reflection on what the market can bear.