Have you called and asked IMS and Bobco? 400 feet is still pretty much small scale retail- probably not worth shipping for a couple of thousand miles. On a small order like that, I depend on my ongoing relationship with my suppliers. When I was in So-Cal (my shop was there for over ten years) I mostly bought from Bobco, and had a first name basis relationship with my salesman- and he, in turn, would track things like that down for me, and bring it in it he had to.
My current suppliers, one for ferrous and another for aluminum/stainless/copper alloys, are similar- I know they will get me a reasonable price for material, and find what I need.
If you are only an occasional walk in customer, you pay retail.
Alum Channel is always a low volume product, expect to pay a pretty stiff price per pound, especially in such a small quantity.
Even in LA, stock may be a problem. Dunno- I try to avoid aluminum if I can, not my preferred material.