I think they took them from other ava versions.
so i do a custom para, but i need help to do my skin and i don't how to do a skin client side. I need some help, anybody can help me? steelskinz and mafia release some skins and ccman32 too... but i dont to bother they
Like @PPCINJ says, the most skins come from versions like kava where they release guns earlier so you cna take the skin easier.