Congratulations, your Pokémon Ruby version has become the meta-game. Perhaps you wish to replace it with 'Body Slam' in such an event as that actually coming to pass. Secret Power was, of course, an interesting attempt at reviving some fairly obscure status effects, and along with Castform had some amount of synergy in the game which was fairly interesting, and might have been worth looking further into. There's probably some fairly fun teams in there, with their own mode and interest. It also has a certain level of interest because, like Hidden Power, it is pretty much not used in certain forms of battle, although in any case this is here explicitly by design, rather than perhaps less explicitly so.
If you really want, you can probably pick it up from Slateport, assuming that you haven't used it yet. If it's not there yet, then you can be fairly certain that the trainer has not yet been met, and hence has not disappeared for that reason. Otherwise, it seems a bit strange that he hasn't appeared yet in your game, at least so far in your playthrough, perhaps he really has opted to follow the smell of adventure and depart from your path. I'm not sure if this is a known bug, anyone heard of such?
