1. Find a Pokemon that can learn Rockslide:
* Geodude: Available in the Rock Tunnel and other cave locations
* Graveler: Evolve Geodude at level 25.
* Golem: Evolve Graveler at level 45.
* Onix: Available in Rock Tunnel and other cave locations.
* Steelix: Evolve Onix with a Metal Coat.
* Rhyhorn: Available in the Rock Tunnel and other cave locations.
* Rhydon: Evolve Rhyhorn at level 42.
* Larvitar: Available in Mt. Mortar and other cave locations.
* Pupitar: Evolve Larvitar at level 30.
* Tyranitar: Evolve Pupitar at level 55.
* Aron: Available in the Iron Island.
* Lairon: Evolve Aron at level 32.
* Aggron: Evolve Lairon at level 42.
* Gible: Available in Route 229 and other cave locations.
* Gabite: Evolve Gible at level 24.
* Garchomp: Evolve Gabite at level 48.
* Shroomish: Available in Route 116 and other grassy locations.
* Breloom: Evolve Shroomish with a Mushroom Bar.
* Machop: Available in Route 24 and other locations.
* Machoke: Evolve Machop at level 28.
* Machamp: Evolve Machoke at level 45.
* Cranidos: Available in Route 226 and other cave locations.
* Rampardos: Evolve Cranidos with a Dusk Stone.
* Shieldon: Available in Route 226 and other cave locations.
* Bastiodon: Evolve Shieldon with a Dusk Stone.
* Roggenrola: Available in Route 214 and other cave locations.
* Boldore: Evolve Roggenrola at level 25.
* Gigalith: Evolve Boldore at level 45.
* Skarmory: Available in Route 35 and other locations.
* Carracosta: Available in Undella Bay and other water locations.
* Tyrunt: Available in Glittering Cave.
* Tyrantrum: Evolve Tyrunt with a Old Amber.
* Amaura: Available in Glittering Cave.
* Aurorus: Evolve Amaura with a Old Amber.
2. Learn Rockslide:
* You can teach Rockslide to these Pokemon by using TM44.
* You can find TM44 in various locations, including Goldenrod Department Store and the Celadon Department Store.
Note: Some of these Pokemon may need to evolve before they can learn Rockslide.