Part 11: Sailed to One Island — Bill's Seagallop
Rock Smash (HM06) is found at the Ember Spa on Kindle Road. Once you beat Blaine, Bill appears on Cinnabar Island and sails you to One Island. From there, the harbor offers Two and Three Island, and Celio's Tri Pass adds Vermilion.
Sailed to One Island — Bill's Seagallop opens 9 areas. There are 28 trainers standing in them.
Where to go
Mt. Ember
Wild: Slugma 100% · Lv 18-36, Geodude 95% · Lv 5-30, Machop 50% · Lv 31-39, Graveler 35% · Lv 30-50 +8 more
Trainers: Crush Girl Jocelyn Lv 38, Pokémon Ranger Beth Lv 38, Pokémon Ranger Logan Lv 40, Team Rocket Grunt Lv 37, Team Rocket Grunt Lv 35
Berry Forest
Wild: Magikarp 100% · Lv 5, Psyduck 95% · Lv 5-40, Slowpoke 95% · Lv 5-40, Goldeen 60% · Lv 5-15 +16 more
Kindle Road
Wild: Magikarp 100% · Lv 5, Geodude 95% · Lv 5-30, Tentacool 95% · Lv 5-40, Horsea 80% · Lv 5-15 +14 more
Trainers: Black Belt Hugh Lv 37, Black Belt Shea Lv 38, Camper Bryce Lv 36, Crush Girl Sharon Lv 37, Crush Girl Tanya Lv 38, Crush Kin Mik & Kia Lv 39 +6 more
Pick up: HM06 Rock Smash
Treasure Beach
Wild: Magikarp 100% · Lv 5, Tentacool 95% · Lv 5-40, Horsea 80% · Lv 5-15, Krabby 80% · Lv 5-15 +11 more
Trainers: Swimmer♀ Amara Lv 36
Cape Brink
Wild: Magikarp 100% · Lv 5, Psyduck 95% · Lv 5-40, Slowpoke 95% · Lv 5-40, Poliwag 60% · Lv 5-15 +13 more
Bond Bridge
Wild: Magikarp 100% · Lv 5, Tentacool 95% · Lv 5-40, Horsea 80% · Lv 5-15, Krabby 80% · Lv 5-15 +15 more
Trainers: Aroma Lady Nikki Lv 37, Aroma Lady Violet Lv 36, Swimmer♀ Tisha Lv 38, Tuber Alexis Lv 34, Tuber Amira Lv 35, Twins Joy & Meg Lv 37
Three Isle Port
Wild: Dunsparce 100% · Lv 5-35
One Island
Wild: Magikarp 100% · Lv 5, Tentacool 95% · Lv 5-40, Horsea 80% · Lv 5-15, Krabby 80% · Lv 5-15 +8 more
Three Island
Trainers: Biker Goon Lv 37, Biker Goon Lv 38, Biker Goon Lv 38, Cue Ball Paxton Lv 39
It also doesn't say when 4 of its areas open up, so they are listed together in the last part rather than guessed into the story.