I ended up going with stainless from what I could find at Home Depot. Simplest solution since the rear needed machine screws and the front needed self-tapping. If they corrode and I have to replace them in a few years, no biggie.
I installed stainless steel bolts and self tapping screws on my 2005 Accord to hold the front and rear plates in place. These bolts were removed when the car was sold and are now on an Accord and our CX-5. No special measures were used to prevent corrosion. After many Chicago winters they still look as new.
