>>96478964
>Is there someone who makes scifi vehicles of a non-gothing-grimdark variety, in this scale?

Rare, but they exist. Stay away from 1/72, as its too small. Check 1/48 kits by Tamiya if you want to go the historical military models route. Alternatives would be Rubicon/Warlord Games for 1/56 plastic kits.
You can get away with 1/35 kits as well, depending on how big your fictional tank should be.

Your best bet for "non-40k"-style sci-fi models is 3d-printing. Check Etsy, and besides the obligatory 50 different Leman Russ variants, you will find interesting sci-fi things as well.