When mine rusted out, my mechanic found this out and got peeved. Called someone he knew in the service center and was somehow able to get just the backing plates. So I suppose if you have a trusted mechanic who is in good with someone, they can be had.
Dorman sells the backing plates.. but there's no levers in them..
the lever is this two-piece jack-leg setup.. according to the Ford dealer I call from at work, you can look it up three ways.. the shoes, the backing plates, and the caliper bracket.. all three pieces supersede into the same part number, which is the assembled unit... left side, $348, rt side $352