When I was a custodian many years ago I used Noxon Metal Polish but there may be better stuff out there now. It was inexpensive and worked quite well IMO.
Purple Metal Magic is available at most Wal-Marts it is as good as Mothers just cost less.
Speedy Metal Polish is Faaaar better than Mothers but since you said over the counter you have limited your options to those mediocre products available OTC.
I've only tried a few (Eagle-One, Mugeuire's, Mothers, and something else that I honestly can't remember. Mothers was by far the best (as was the Mothers chrome cleaner spray) that I have used on my wheels.
I recently used Mothers Chrome Polish on some wheels with black spots and did a nice job. I think one key is using a terry cloth type towel since it has extra bite of a "rag" or microfiber towel.
Mothers can also be used on exterior glass to remove water spots.