Where do you find flash in Pokemon Ruby?

At Dewford, go into the cave at the east side. When in there there should a hiker, talk to him and he’ll give you the HM Flash.

Where is TM 43 in Pokemon Ruby?

Game locations Red​/​Blue Victory Road Gold​/​Silver Lake of Rage Ruby​/​Sapphire Route 111 (north; from guy in front of tree) Slateport City (Slateport Market – $3,000) FireRed​/​LeafGreen Route 25 (northwest) Celadon City (Department Store – $3,000) Diamond​/​Pearl Amity Square (south).