These are some places you can find rare candies through out the game without cheating.

1. Mt.Moon - 1st floor
2. Cerulean City - Above the badge descriptors house in the grass.
3. SS.Anne - In one of the rooms.
4. Lavender Town - Top floor, hidden behind the stair case of where the ghost appears.
5. Rocket Hideout - There is a rare candy in both celedon and Saffron hideouts.
6. Cycling path - Beside one of the signs.
7. Fuchsia city - Inside the wardens house.
8. Pokemon Mansion

These are just some of the rare candies, there many more hidden throughout the sevii islands like the ones behind the move tutors house in island two and the one in the caves by resort gorgeous on island five.You can find the rest!