I did a "waht if" Challanger I with this camo eons ago. I seem to remember using Fs 30140 and 16231, but can't find my references. This sound 'bout right?

I found that Humbrol 79 Blue Grey or Lifecolor UA145 was closer to my reference photos for the grey but the brown sound right.
I have also included a couple of options for you on the colours.

FS:30140 Brown Special
Lifecolor UA085
Model Master 1736 Leather
or a couple of mix
Humbrol mix 4 parts 110 Matt Natural Wood, 2 parts 62 Matt Leather, 1 part 113 Matt Cream
Tamiya XF52 Flat Earth 1 part + XF64 red brown 1 part

36231
Humbrol 140 Matt Gull Grey
Or mix
Tamiya XF-83 Sea-Grey 1 part + XF-66 Light Grey 1 part + XF-54 Dark Sea Grey 1part + XF-2 Flat Black 3 parts

Ammo by Mig also makes Berlin Brigade set of paints.

The color by ammo is good for end of time in Berlin, system issue paint
the start of the camo was a darker gray and brown which were a local buy.