Since I don't know anything about the WTS API personally, there are three places I'd check for developers:
1. RentACoder.com
2. ELANCE.com
3. ODESK.com
I've had good luck with the first two for stuff I needed coded. You're liable to find talent there is a bit cheaper since many folks are independent rather than associated with a a firm and all their overhead.
With all three sites, you tend to get a lot of form replies where they don't even bother to read your request - just don't be discouraged by that. Rentacoder has a feature that tries to prevent that so I like using that site and is usually the first place I go for developers. If I can't find any there, then I try ELANCE. ODESK is one I haven't used for many moons but I did use it at one point a few years ago.
Hope this helps. Let me know how it goes.