HM04 (Strength)

Kanto
Fuchsia City, given by the Safari Zone Warden after returning him his Gold Teeth. Reqires the Rainbow Badge to be used out of battle.

Hoenn
Rusturf Tunnel, from Wanda's boyfriend after the rocks blocking the middle of the tunnel are smashed. Reqires the Heat Badge to be used out of battle.

Sinnoh
Iron Island, from Riley when the player first arrives on the Island. Reqires the Mine Badge to be used out of battle.

Unova
Nimbasa City, from an Ace Trainer in the building northwest of the Pokémon Center.