\World of Tanks\res\packages\gui-part1.pkg\gui\maps\vehicles\decals\
\World of Tanks\res\packages\gui-part2.pkg\gui\maps\vehicles\decals\
Can be opened with 7-zip for example.
Knock yourself out. 🙂
Can place the .dds files into res_mods afterwards, for example:
\res_mods\VERSION\gui\maps\vehicles\decals\