The only Southern Cross model kits I've ever seen were for the personal armors of the main characters.
That said, if you search deep enough you can find things like this:
(It's a Frankenstein build made of several mecha kits.)
Google is your friend:
(Granted, it doesn't have the hovertank mode -- I thought you could fold the legs and at least get an approximation of it.)
Way back in the 80s, when I was still a lad, I bought the Battletech boxed set because, duh, giant robots. We set up for that first game and got completely owned by my friend in his Shadow Hawk.
Turns out we thought heat was the sole moderating factor in weapon fire. Shoot as many times as you...
Dream Pod 9 is coming up with a new starship combat game set in the Jovian Chronicles universe. Get the Beta rules free here:
Check Google, there are a few examples of Guardmen models with Tau Firewarrior torso, gun, and arm shield. I remember someone using upper legs as well to get the lower armor, cutting off the Tau feet and replacing them with Guardsman boots. Works well.
The book was not published, no (at least as far as I know).
There are semi-official beta rules for the Phalons here:
I've never seen rules for Kra'Vak, but I'm sure they exist somewhere on the Web...
UPDATE: I knew I'd seen them somewhere...
If you have money to buy an entire chapter's worth of minis, you have enough money to get someone to paint them for you. Multiple times, if you suddenly decide you don't like the color scheme anymore. ;)
The double-whammy of recently losing my job and having to do home repairs this Spring means I need both space to work and money. It's thus time to liquidate the game books that have not been opened for a while.
Make me an offer and let's talk. My loss is your gain!