Pallet, Viridian - 2 slots
Route 22 - 2 slots
Cerulean[+gym], Routes 4/24/25 - 3 slots
Vermilion[+dock], Routes 6/11 - 2 slots
Celadon, Route 10 - 2 slots
Safari Zone - 4 slots
Routes 12/13/17/18 - 4 slots
Cinnabar, Routes 19/20/21, Seafoam - 4 slots
Route 23, Cerulean Cave (Mewtwo Cave) - 4 slots
Fuchsia - 4 slots