Check out coast aluminum.
www.coastaluminum.com
They are in Santa Fe Springs. Check out their online catalog but also call to see if they have anything new or different.
We have purchased both 1x2 and 2x2 .062 wall locally here in LA.
The likely hood of finding something like 7/16 x 1-5/8 is very slim.
You can also check out Fry Steel, and Industrial Metal Supply both have locations in the LA area.