C-Gear skins are saved into the save file, with encryption as you already know. PokeCGear exports these (probably encrypted) skins in a format ".psk". Poke Skin or whatever. C-Gear skins are 256x192 pixels and can also be exported to bmp format.
Over at Project Pokemon you can find this PokeStock and the translated version, in addition to the C-Gear Skin Exchange Thread where you can download past skins or upload new ones.
C-Gear Skin Exchange Thread
PokeStock Main Download Thread
Kaarosu's Translations of the Subprograms Thread
Hope this information helps in whatever you are trying to do
This is useful, thanks alot. If we could find the way how it exports the PSK as a BMP, we could reverse it, exporting BMPs as PSKs and adding custom C-Gear Skins. I'll look into it