Here is a list of the real-world weapons that BRINK's guns are based on. This is changeable and debatable.

Pistol:
Kalt Pistol - USP .45
Sea Eagle - Desert Eagle
Tokmak Pistol - Beretta M92FS
Ritchie - .357 Revolver
Bolgo MP - Glock 18

Light:
Drognav - M21
Barnett - Barrett
Kross SMG - Vector aka Kriss Super V
Bulpdaun - Tar-21
Tampa SMG - Steyr TMP
Carb-9 SMG - I have no idea. Bizon comes to mind though.

Medium:
Mossington Shotgun - Mossberg 500 Tactical Shotgun
Rokstedi AR - Scar-H
Euston AR - Colt M4 Carbine
Gerund AR - Bushmaster ACR
Rhett AR - No idea again.
FRKN-3K AR - FN2000 (ironically, it has slow 3-round burst instead of fn2000's superhigh fire rate)
Lobster GL - M79 Grenade Launcher

Heavy:
EZ-Nade AGL - MGL-140
Chinzor MG - don't know.
Maximus MG - M249 LMG
Gotlung Minigun - Vulcan cannon
Hjammerdeim Shotgun - Pancor Jackhammer full-auto shotgun (although Hjammerdeim has 2-shot and a delay instead)

There ya go except the unknowns which I need you to identify.

Hehe, yeah, they certainly had inspiration from real life I guess

You missed the Galactic SMG which is obviously the UMP-45. Universal Machine Pistol.

http://www.gamesas.com/index.php?/topic/1173072-brink-weapon-derivitives/page__hl__m4a1

Eh, the Ritchie has far, far, far more kick then a .357 it reminds me more of a short barrel S&W .550 bear gun.

EDIT: Oh look KidEx18's post does it all, but better!

The Bulpdaun is actually based on the Magpul PDR. If you add a foregrip it's nearly identical.