Aha!
It's been bugging me since I mentioned it, but I've finally found the other space hamster picture I was half remembering from a day or three back. The reason I wasn't finding it is because it's not MgT2, it was a 1st edition Third Imperium product called 'Into the Borderland' with the critter on the cover and p.15. (The colour cover was what made me think it must be MgT2). It's called a steakhamster so I was actually closer than I thought to having the right kind of critter!
Anyway, I don't suppose anyone cares but that's my complete list of Traveller's space hamsters:
MgT1
Into the Borderland, p.15ff & p.36 - Talkan's Grazer or Steakhamster
MgT2
High and Dry, p.10 - Walston
Spinward Marches 1: The Bowman Arm, p.13 - Walston
Although I should note that Steakhamsters are "unbelievably stupid" and "completely untameable" - so probably not much use as a mount even though they're cow sized. The walstons would be too small to ride.
And that will probably be the shortest bibliography/index I produce for Traveller. You saw it here first. :-)
tc