There is a company right here in Spokane that does hot galvanizing but they only treat parts they manufacture, sadly no amount of begging will get them to take on a small or even a moderately large run of car parts (muffler shields, license plate holder mechanisms, brake dust shields, etc.). Trust me, I've tried.

*The Spangle size on the A-body backing plates I've seen is a smaller size, roughly 1/8-1/4" or so splotches.