All locations are directly quoted from Bulbapedia because I wouldn't be able to write them more succinctly.
Route 2
North of the western grass field, near the entrance to Accumula Town
Route 3
(1) In the north of the dark grass
(2) The northern portion of the pond (requires Surf)
Route 5
To the right of the trailer
Route 6
(1) In the southwest, north of the Pokémon Breeder
(2) In front of the entrance to Mistralton Cave (requires Surf)
Route 7
To the right of the house on the left
Route 9
To the left of Shopping Mall Nine
Route 13
(1) Southwest of the two cuttable trees
(2) At the top of the stairs towards the entrance to Giant Chasm
Route 18
To the south of the Hiker
Route 22
In the northern part that is only accessible using the walkways
Route 23
West side of the river on the upper level near the entrance to the Giant Chasm
Pinwheel Forest
(1) Left of the body of water under the pair of bridges (interior area) (requires Surf)
(2) Near Challenge Rock (exterior area)
Giant Chasm
Near the entrance to the forest
Abundant Shrine
(1) Near Youngster Wes
(2) Right of the shrine, across the water
Lostlorn Forest
In the northeast at ground level, to the right of where TM95 is found
Floccesy Ranch
In the northeast corner (requires Surf)
Hidden Grotto Locations (Bulbapedia)
