Instructions
Travel to Viridian City. Viridian City is a small city in the west of Kanto. It is situated between Pewter City to the north and Pallet Town to the south. If you have been to Viridian City before, you can fly there instantly using HM02 (Fly).
Walk west on Route 22 from Viridian City towards the Indigo Plataeu. You will eventually reach the Victory Road tunnel. Bring some Repel items with you to deter the masses of frustrating, time-wasting Zubat that spring up in caves. Also bring an Escape Rope, in case your Pokémon are struggling. Be careful of other trainers while traveling through Victory Road; if you are not prepared for them, they can wipe you out. Once you pass through Victory Road, you will be on Route 28.
Walk around the long grass of Route 28. Be alert; wild Pokémon attack randomly in long grass. Keep walking and soon a level 40 Donphan will appear. Donphan are quite easy to capture; you can catch a weakened Donphan using a Poké ball.