Sorry Supersonic, but your information is not correct. Leppa berries are quite common and can be found on many routes. What you are thinking about is the LIECHI Berry that can ONLY be found on Mirage Island. As I am a berryholic, I have compiled the following list of where you can get each berry. Keep in mind that the people listed for each berry will only give you ONE berry per day, with the Berry Master's Wife the lone exception (read about her at the bottom):
1. Cheri: Route 103-104; Flower Shop; BMW; man in Lilycove
2. Chesto: Route 116, 121; Flower Shop; BMW; man in Lilycove
3. Pecha: Route 102, 104, 112, 123; Flower Shop; BMW; man in Lilycove
4. Rawst: Route 112, 121, 123; Flower Shop; BMW; man in Lilycove
5. Aspear: Route 120-121; Flower Shop; BMW; man in Lilycove
6. Leppa: Route 103-104, 119, 123; Flower Shop; BMW; man in Lilycove
7. Oran: Route 102, 104, 111, 114; BMW; man in Lilycove
8. Persim: Route 114, 121; BMW; man in Lilycove
9. Lum: man in Lilycove
10. Sitrus: Route 118-119, 123; BMW; man in Lilycove
11. Figy: Trainer ID ends in 0 or 5; Kiri in Sootopolis
12. Wiki: Trainer ID ends in 1 or 6
13. Mago: Trainer ID ends in 2 or 7
14. Aguav: Trainer ID ends in 3 or 8
15. Iapapa: Trainer ID ends in 4 or 9; Kiri in Sootopolis
16. Razz: Route 111, 120; Girl on Route 111; Boy on Route 114
17. Bluk: Route 115; Boy on Route 114
18. Nanab: Route 110, 120-121; Boy on Route 114
19. Wepear: Route 117, 120; Boy on Route 114
20. Pinap: Route 116, 120; Boy on Route 114
21. Pomeg: Route 119, 123; BM; Kiri in Sootopolis
22. Kelpsy: Route 115; BM; Kiri in Sootopolis
23. Qualot: Route 123; BM; Kiri in Sootopolis
24. Hondew: Route 119; BM; Kiri in Sootopolis
25. Grepa: Route 123; BM; Kiri in Sootopolis
26. Tamato: BM; Kiri in Sootopolis
27. Cornn: BM; Kiri in Sootopolis
28. Magost: BM; Kiri in Sootopolis
29. Rabuta: BM; Kiri in Sootopolis
30. Nomel: BM; Kiri in Sootopolis
31. Spelon: BMW
32. Pamtre: BMW
33. Watmel: BMW
34. Durin: BMW
35. Belue: BMW
36. Liechi: Route 130
37. Ganlon: Pokemon Colosseum, Jirachi Bonus Disk
38. Salac: Pokemon Colosseum, Jirachi Bonus Disk
39. Petaya:
40. Apicot:
41. Lansat: Get all Battle Frontier Silver Symbols
42. Starf: Get all Battle Frontier Gold Symbols
*BM - Berry Master, BMW - Berry Master's Wife
Lastly, here is the list of phrases to tell the Berry Master's Wife in order to get one of the extremely rare berries. Remember that you can only get these ONCE. If you ask her the phrase again, or any other phrase for that matter, you will randomly get one of the first 10 berries.
Spelon Berry - Great Battle (default)
Pamtre Berry - Challenge Contest (must obtain Contest Pass)
Watmel Berry - Overwhelming Latias (must have encountered Latias)
Durin Berry - Cool Latios (must have encountered Latios)
Belue Berry - Super Hustle (defeat the E4 at least once)