3 liveries for SkylineGTRFreak's ZSU-23, Tan (a requested livery), Green and Tan, Green and Brown, no specific armed forces.
The base ZSU-23 is here: https://www.gta5-hub.com/vehicles/zsu-23-4m4-shilka-add-on

Note: Because of a texture fluke, it appears the additional liveries always use the wheel texture from zsu23_sign_1, so the Tan livery is in an exclusive .ytd file in the ShilkaTan folder.

Once installed with their instructions, open the dlc.rpf with OpenIV

Follow this path to the file to overwrite:

...\GTAV\mods\update\x64\dlcpacks\shilka\dlc.rpf\x64\levels\gta5\vehicles\vehicles.rpf\shilka.ytd

I typically extract the original .ytd to the same folder as the dlc.rpf and rename it to origshilka.ytd.

When ready to overwrite with the additional liveries, toggle "Edit mode", top right button, and drag shilka.ytd from the extracted zip file and drop here:

...\GTAV\mods\update\x64\dlcpacks\shilka\dlc.rpf\x64\levels\gta5\vehicles\vehicles.rpf\shilka.ytd

Just to confirm the livery, I'd click on the shilka.yft or shilka_hi.yft file to open the OpenIV Model Viewer to see what the model will look like with the new livery.

Once satisfied, close the model viewer and run GTAV and spawn shilka with the trainer of your choice.

I've included my work files in case you'd like to use it as a starting point for your own work.

Enjoy,
Gillman