From Pallet town surf South and it should be there.
surf at the south of pallet town
surf through passage ways in front of the island
first you go to Cinnabar Island then surf to Sea Foam Islands then find your way throw
You cannot literally get 'into' Cinnabar Island, but only stay 'on' it. You have to surf south of Pallet Town to get to Cinnabar Island. You cannot go south of Fuchsia City due to construction.
Since you are already able to surf, you could go either the classic route to Pewter or surf to Cinnabar, which has erupted. The gym moved to the nearby islands, up the ladder.
You can go up from cinnabar island using surf or go down from pewter city .You can use headbutt in pewter city and get a starly.
The Cinnabar Island
beat the power plant and then beat snorlax go through digletts cave beat gyms go to pallet town then surf in an instant your there
have to get surf from Johto, then go to Pallet town.Then go south.
earn all 8 kanto badges then go see professor oak in pallet town. after that he gives you HM 08 rock climb. then you surf to cinnabar, use rock climb all the to the top
On Pokemon soul silver the cinnabar gym is located inside Seafoam Islands.