Collectibles
Are you talking about armor? The only ‘collectible’ slots for armor are in the PvP locker.
The armor skins in the gemstore can be converted for PvP use. When you initially apply to armor you are prompted with “Use Normally” and “Convert to PvP”. I imagine the latter would make it possible to deposit them in the PvP locker. So I say check there too, just in case.