You need to track down the .VMT and .VTF files for the model, some models use more than one, the .VMT as with world textures determines which .vtf file is used, usually the model textures are under textures/models/ in the same directory as the .mdl file. VTFEdit by nem's tools can export textures in .tga, .png, or .jpg.
In terms of the invisibility, you want to export the texture as a .tga to retain the alpha channels
also I'm guessing you know but the models and textures are sometimes in different .vpk files
[Hazmat]
Hazmat joined
[Redacted]