The HM Surf can be found in the Safari Zone of Fuschia City in "Pokemon LeafGreen." Head to the northwest corner of Area 3, and enter the Secret House to receive the HM03.
When players enter the Safari Zone, they are given 30 Safari Balls to catch Pokemon and a maximum of 600 steps. To reach the Secret House, go east from the main entrance to Area 1, and cross over two cliffs northwest to Area 2. Find the exit in the southwest corner of this area and grab the Gold Teeth to later receive the next HM, Strength, later on. Enter the Secret House, and speak to the man inside to receive the HM.
This powerful move can be taught to most water-type Pokemon as well as some ice-type Pokemon. Although it can be taught and used in battle immediately, it cannot be used to cross bodies of water outside of battle until the Fuschia City gym leader Koga is defeated and the Soul Badge is received.
Other items that can be found in the Safari Zone include TM37 Steel Wing, TM11 Sunny Day, TM32 Double Team, Quick Claw, a Leaf Stone, a Max Potion and Protein. The area is also home to exclusive Pokemon such as Tauros and Kangaskhan.