You should be able to find those in any decent hardware store. I believe I have seen them in the bins they have in our local hardware.
I recall that mine (also the "Chevrolet" emblem used on '51's) had the "hat" style nuts on them - a hex nut stamped out of spring steel with an integral washer, similar to
these but not push-on. I'd have to dig them out of my parts storage box to verify though.
