EA,
I can tell you why Hobbytown here in town doesn't buy a lot of "outside" parts: The pile of checks she writes to all the different suppliers every month is staggering.
She tries to always buy through her existing distributors to keep her life simpler...to the extent she can.
If you want to sell things through hobbyshops, if my local shop's POV is any indicator, the way to do it is to sell through GPD, Horizon or some other distributor that has good coverage. Even a smaller one that has some key products would work (racer's edge?).
It may be a "simple order" with good pricing, but the book-keeping on the other side of it adds up quickly.