The Safari Zone Gets an Upgrade After you defeat the Elite 4. 2 More Areas to the right of the entrance are opened up.

These 2 Areas Contain a vast array of GSC Pokémon...and to make it even tastier, most of these have been unavailable in games previously without having to breed Colosseum Pokémon
You're Going to need the following things to get the best use out of these areas: HM06 Rock Smash, HM07 Waterfall, HM03 Surf & A Super Rod

Wild Pokémon in Safari Zone's New Areas

Here are the Pokémon you will find in the wild in Safari Zone's New Areas:

In The Area 1's Grass
Sunkern Common
Mareep Common
Aipom Uncommon
Spinarak Uncommon
Hoothoot Uncommon
Snubbull Uncommon
Stantler Rare
Gligar Rare
In The Area 2's Grass
Aipom Common
Teddiursa Common
Sunkern Uncommon
Ledyba Uncommon
Hoothoot Uncommon
Pineco Uncommon
Houndour Rare
Miltank Rare
In The Area 1's Waters (Surf)
Wooper Common
Marill Common
Quagsire Rare
In The Area 1's Waters (Fish)
Remoraid (Super Rod & Good Rod) Common
Octillery (Super Rod) Rare
Magikarp (Old Rod & Good Rod) Common
Goldeen (Old Rod & Good Rod) Common
In The Area 2's Rocks (Rock Smash)
Shuckle Common