Within the Safari Zone north of Fuschia city there are several houses you can go into, but you are looking for the Secret House in particular, where a man will give you the HM03 (Surf)
Directions
You need the related link of the FULL MAP in order to do this properly
~ Start in Area 1
~ Proceed to the East exit to Area 4
~ Make your way to the North West Exit to Area 2
~ Walk around the route to the furthest exit on the left and enter Area 3
Chat with our AI personalities
Surf is HM #3. :-)
Get the HM Surf then teach it to a pokemon.
hm suft is in the secret house at the back end of the safari zone
teach it the HM surf
you must traverse all the way thru the safari zone