I'll back up Ross' comment on that Tamiya Flat Sky Gray, XF-19. As long as you give it time to dry it seems to stick really well. I actually just used this technique last weekend thanks to Ross' suggestions in another post.
As for Tamiya, I contacted them in regards to supplying us with an acrylic primer and they gave me the short answer as usual. And that is, "no we don't carry it and we don't plan on it."