List of reskinnium series in the game, which is what you're pretty much guaranteed to get at ranks 51-59:
Black Eagle
Claw
Eraser
Fox
Hades
Hi Tech
Ice
Joker
Merc
Monster
Neon
Phoenix (only 3)
Reaper (only 2)
Saw
Shark
Solar Serpent (only 3)
Storm
Thunderbird (only 3)
Wolf
Note that this list is not intended to include all possible reskinniums - there are dozens of "single" versions such as the T-72AV Ash and T-64AV Hunter that are the only examples of their particular reskin. Each of the above series contains at least 4 vehicles.
If you know of more that I'm missing, let me know and I'll add them to the list.