You will get it from Wally's father beside your father's gym after beating your father.
You can get Surf at Wally's house after you beat Nomad. He will say that something about Wally's parents having something to give you. Go to his place and you can get it by talking to them.
maybe..defeat the fourth gym leader(Norman)..
surf surf surf.
Just put another Pokemon with surf in your party
Goldeen
surf to mount pyre then beat team aqua/magma then you can surf to team aquas hideout from lylicove after that the wailmers wil move and you can surf to modsep
You beat your dad in petalburg and the house beside it you get surf.
Pokemon cannot forget HM's unless they're in Pokemon Mystery Dungeon. But, if its from Emerald, add another Pokemon to your party that knows surf and ask the move deleter.
after you beat your father's gym
After you battle your dad in petelburg
yes
No Armaldo cant learn surf SuperM1854
easy just teach a Pokemon surf