From Siberakh1 in another thread:
Ladybrooklyn (she doesn’t really post here much… I’d have to see if I could find her on AIM) does model horse painting with powders. She’s the one I’ve learned how to use powders and how to dapple from. I’ve never done a Breyer model myself (just Windstones), but I know she does Breyer and a few other equine models. I’m not sure what her schedule is though.
Her Windstone profile: memberlist.php?mode=viewprofile&u=183
Her website of her work: http://community.webshots.com/user/desertsunstudios
I don’t know what her rates are, but it never hurts to ask.