very very rare
They are rare in route 7 and the safari zone
You can get a Riolu in the Safari Zone-even though they are very rare. From there, evolve it into Lucario.
It is rare in the Blackthorn side of the Dark Cave, Cerulean Cave, and in the Safari Zone.
You cant catch Lucario but you can catch Riolu & evlove it: After you gain ownership of the safari zone, Put the meadow block in the map and put 10 forest blocks (tree) and 14 peak objects (rocks) and it will be there. (very rare but it is there trust me i know.
In the Safari Zone(Encounter Rate is rare)
In Pokemon Soulsilver and Heartgold you can get it in the safari game. For Diamond and Pearl, you can get it in the trophy garden but it's rare. You can also get it in Black and White somewhere (can't remember), but it's rare too. The most easiest way to get Jigglpuff is by going on the safari game in soulsilver and heartgold on the ds.
They help you catch rare Pokemon such as duskull and riolu. For example: I caught my duskull using peak objects in the swamp area.
To get Larvitar, you can either go to a certain area of the Safari Zone (where they are extremely rare), or you can go to Mt. Silver and try to find one there (they are still rare).
Not really. Bagon is a slightly uncommon Pokemon to find in the wild (similar to Larvitar), and Shelgon just evolves from Bagon. Its not that hard to get. Shelgon is only rare in the Safari Zone of HeartGold/SoulSilver.
There are a few rare Pokemon you can get in the safari zone they are pinsir, wobuffet and girafarig.
Croagunk, Noctowl, Hoothoot, Psyduck, Quagsire, Starly, Staravia, Azurill, Marill, Skorupi and each day, there will be one specific really rare pokemon.
Yes, it is possible to obtain a Salamence. You must first catch a Bagon and train it to level 50. Bagons are extremely rare in the Safari Zone.