I don't know of any PBEM versions for the Mac...but you can run Windows on a Mac and then you would definitely be all set with Cyberboard. Or if Vassal has a module for the game, then you can run that on a Mac for sure since it runs under java.
Gosh, I remember playing those Balkoski Fleet games. Yup, I liked those you listed better than 5th Fleet (and I never played 3rd Fleet...). Of them all, I loved 2nd Fleet the best, although 7th wasn't too bad either. Think Steve Jolley plays the Fleet games!