I actually went and decompiled the model to find the path for textures and its this:
zarp_ssrp_content_652459719/materials/models/weapons/rinfect
You will not want to touch the vtf file with the '_n' on the end, as that's the bump map (i think) and has nothing to do with how the gun will be colored/textured, it adds to the bump detail.
Gluon:
zarp_ssrp_content_652459719/materials/models/v_egon
Juggernaut Suit:
zarp_ssrp_content_652459719/materials/models/shaklin/payday2/dallas