Expanding on what Dave posted above, a Star Trek themed train in '0 'gauge would have to be custom built right now. An HO set seems to have been produced in 2009, although it was a subscription item.
Notice the prices of the items, which are about half the size of '0' gauge, and also 6 years ago.
Although there may be many train enthusiasts that would want a Star Trek train, getting one commercially produced would need first to get a market survey to see what kind of market there is for such a product.
Next, licenses must be procured ($$$) to use the images and names in a product.
Designing and manufacturing the appropriate tooling dies and molds would add more money (LOTS) to the equation.
After all this is done, the first Star Fleet commissioned train would roll off the assembly line.

For now, "Beam me up, Scotty, there's no '0' gauge Star Trek trains down here"!

Larry