ty but i still can't find a way to Motrient City, i dived everywhere and ended up finding Ho-Oh in Hunter's House, i kept diving and coming up and it's getting annoying :( and i don't find the legendaries hard to catch, in fact i caught Raikou with a great ball :P cuz i just use save states, when i fail i just load and i'm back to the the point when i'm about to use a pokeball, instead of trying to damage him all over again.
i may be wrong, i haven't even finished the game yet but correct me if i'm wrong (btw u need the 8th badge to catch most of the legendaries i think)
1. Jirachi is somwwhere near Tabuli Town, and just below the town u can find the Fire Cave where Entei is, it's just near Ash's cabin where he gives u dive.
2. Ho-oh, Zapdos, Articuno & Moltres are all below Cinnarbar Isle, for Ho-Oh u have to use dive and then when u come back up the surface on another side u'll find a path going upwards like a hill and it'll say Hunter's House. For me i didn't have to get the 8th badge to fight it, which is weird cuz all the other ones you do.
3. Suicune is in the north cave i think, just north of Snow-Soft Town where ur brother's gym is. U have to wait till the tide is low to get to it.
4. Raikou u'll encounter easily, when Alex asks u to shutdown the power generator from the power plant place, u'll find him there.
currently i've only caught Raikou (with a great ball :P) and Ho-Oh, so i may be wrong but that's what i've read and learned.