In Mossdeep City, Steven's house is in the top left corner. I had the same problem. I suggest training in the ocean, right on the shore of Mossdeep, if you think your Pokémon are strong enough you can battle Gabby+Ty the TV interviewers until their Exploud and Magneton are level 39. You can battle them north of Mauville just north of the rocks. Then, surf east of Mauville and when you hit land you will see them almost instantly. Last, go east of Fortree City on route 121 and just before you go into the grass and search for them if you need to. They rotate in that order, however if you've already battled them you need to search those places first. Anyway, I'm sorry I made this so long but my main point is that you must battle the gym leaders Tate+Liza in Mossdeep then go to the space center place and when you clear all the grunts and Maxie, visit Steven he has something for you. :)
Dive is not an HM in firered but if you trade a Pokemon that can learn dive to ruby, sapphire or emerald then teach it dive then trade it back it will still have dive however you cannot use it outside of battle.
You get the abilty to use the move Dive from Tate and Liza in Mossdeep and then you can teach your Pokemon to Dive! X3 POKEMON-1001
Go to the top-left corner of Mosdeep city and go inside the house. There's Steven, who will notice you and give it to you
you dive at route 128 by sootopolis city
Since dive is not a HM in firered you will have to trade a Pokemon to a friend that has ruby, sapphire or emerald then using that game use the HM Dive to teach the move Dive to that Pokemon trade it back so firered can have that Pokemon again it will still have Dive however you cannot use it to dive underwater.
go to Stevens house at mosdeep city i think it was?
At the start of the game, there is a choice between three Pokemon to choose. Mudkip can learn dive as he is a water/mud Pokemon. Another Pokemon that can learn dive is kyogre, which is at the end of the game. Any water Pokemon should be able to learn dive, surf and waterfall though.
To get to Stevens house,fly to Mossdeep city if your already there go to the Pokemon center then head left 7 steps then up 6 steps then right again 2 steps then up 2 (it should take you to the middle house of three) then go in the house.that should be Stevens house(that's where you het the HM dive)
get rayquaza
after you beat the mossdeep gym you have to go to the space centre and fight team magma with steven. after you beat them, you go to Stevens house in mossdeep city and he will give you TM 7, dive
go to Stevens house and he'll reward you with the HM dive
it is on the island with the phsycic gym twins leader and where you get dive with the rocket tower/silho
Im Mosdeep City, visit Stevens house. It is the Northernmost house of the left, NW of the PokeCenter. In there you will talk to steven, and he will loan you HM 08 Dive.
Dive is not an HM in firered but if you trade a Pokemon that can learn dive to ruby, sapphire or emerald then teach it dive then trade it back it will still have dive however you cannot use it outside of battle.
HM08(Dive) can be found at Steven's house after clearing the Space Museum in Mossdeep City. Steven's house is north of the Mossdeep Pokemon Center.
You have to have a Pokemon in your party which know the HM Dive. Surf onto water then go to your party, select the Pokemon that knows dive, and click on Dive.
You get the abilty to use the move Dive from Tate and Liza in Mossdeep and then you can teach your Pokemon to Dive! X3 POKEMON-1001