All of the pokemon packs that I have been able to find don’t have every pokemon, and while I am fine with that, I have a personal use for this trio, especially terrakion.
There’s a reason why those Pokémon haven’t been ported yet. All the ones which have been ported were from either PokéPark game (which have a known model format that can be exported easily) and Battle Revolution, which has to be rigged manually. The only game the “musketeer” trio appears in is PokéDex 3D, which is currently impossible to rip from like any other 3DS game. The iOS PokéDex app which was released recently is currently a mystery since nobody’s dumped that yet – maybe it can’t?
Either way, the only way they could be done is if they were custom-modelled.