I believe that to qualify with Stuller you simply need to have a resale number and submit an application. They deal with the size of one's operation/purchases by the fact that when you buy items in larger quantities they cost less. As for Fed Ex, the reason that they only ship with them is that they have negotiated extremely good terms with them and therefore the shipping is quite reasonable considering the fast service. Many retailers have "issues" with Rio Grande because they sell to the public for the same price as to those in the trade.
Another approach that may be worth your while would be to find a studio goldsmith who works with higher karat golds and see if they will make some for you.
Marc
http://www.flyrodjewelry.com/home.html