The Megaminis releases include several ships and a pack of Droyne. BIG Droyne.
The Traveller Universe really supports three scales of conflict: RPG, Army actions, and Navy actions. RPGs seem to work best in 25-28mm, though 15mm also works, particularly for actions aboard ships. Army actions (as seen in Striker) really top out at 15mm, but could readily be done in 10mm or 6mm. Navy actions (spaceships) vary from "dueling lifeboats" up to the Happy Fun Ball (Tigress) and bigger.
Going backwards, I'm not really worried about ships, as the number of starship miniatures lines in production is, frankly, staggering.
Back to RPG scale, I can also scare up sufficiently generic SF types in 25-28mm to make my games work. I'd dearly LOVE to have a few more distinctly OTU minis in this scale range, but I can make do.
For military stuff, the prospects are rather bleak. Despite a surprisingly large body of 15mm SF out there, the potential of the scale is still barely being touched, Traveller or otherwise. There is also a fair bit of 6mm, and even 2mm, SF out there, but little of it is really applicable to Traveller.