I did a bit of research, but didn't come up with much. Osprey MAA 216 - Red Army of the Great Patriotic War, is my only refference.
You were right about the border troops and their bright medium green branch colour. Now about the pink of the Internal Security troops, I did not find any evidence. Some 2 decades ago, I remember reading some Sven Hassel book were there were some similar descriptions of NKVD fur hats with some yellow-pink insignia.
To make the soviet figures in 1/72 look like NKVD, I suggest you use peaked cap heads, from WWI russians or early british, as even the privates had them. Similar to WWII british Military Police.
The branch colour of NKVD was from 1943 sky-blue, worn on the peak of the cap at least by officers, with red band and red piping (as opposed to the infantry, who wore raspberry). Shoulder boards were blue. I think the Alanger SMERSH are as described in Osprey.
For your red army, did you also paint some komissars or politruks?

hi Radu...yes i did see the blue and red caps as NKVD. so i may paint a few officers as such. as it is, my soviets army is small but growing. at present i have 6 hat t-34s, 5 corgi t-34s, some artillery and trucks, and my infantry is organized as such: revell and italieri are guards, esci are a motorized rifles unit, and the siberians are only used for the 'winter' phase of my campaign game. i have some old airfix infantry which look so pitiful that they are a penal company. the NKVD troops are atlantic russians. i also found a set of soviet tankers by LW. and the revell cossacks (my favorites). at least one of each of every set but i'm planning on expanding this army. for years i concentrated on the western front. i think pegasus new releases will give the soviets a shot in the arm, interest wise. the nice thing is they are not hard to paint. simple uniforms and equipment. i made a nice winter scene as a place to display the siberians and caesar germans. as far as kommisars, you gave me a great idea! thanks again for your help!

The kommisars had light blue caps and trousers, and red stars on their sleeves.
Is there a difference in scale between the T-34 from Hat & Corgi? Is it noticeable?

Thank you,

radu

hi Radu...the difference between the corgi and hat t-34s is great, size wise. the hat t-34s are huge in comparison to the corgi's. so i never brigade them together. the corgi's look more like H0 scale, hat are real 1/72. so i use the hat t-34's with italieri and revell russians, and corgi t-34's with airfix and atlantic troops. keep in mind, i use them for wargames, instead of actual dioramas. and if they're dropped off table, no damage. i merely wanted to build up my soviet armor rather quickly, so the corgi's work for now. the hat t-34s are a great idea for building large formations quickly. i still use some actual models made from years past, but they suffer real time damage and are a pain to maintain. highly reccomend the hat t-34's. i drilled the turret cupolas out and now they have commanders. cool!