I think that the Starfleet Battles/Zocchi Minis is officially 1/3900, which is a case of "close enough for marching band" as the sculpts were originally done in the late 70s before the references we currently have were unavailable.
Also, as you'll notice if you study them closely, the miniatures are based on Franz Joseph's Starfleet Tech Manual
. That's how the makers of SFB stay out of licensing disputes- their product is based on the FJ book, rather than the version in the series (which is also why you'll never see movie or later generation ships in SFB).
Hey, it's weird, but the game's been out for 30 years, so it must work.
You can look at their entire line here
. Some are really neat, some don't thrill me so much, but take a look.