Throwing Rocks seems to be best. If you can get it angry on the first turn, it's much easier to catch. Check where you're searching also. There are two areas where the rares appear, in one they are 1% of the encounters, the other - 4%

Pokémon -------- 1% -------- 4% -----
Tauros -------- Area 2 ----- Area 3 ---
Chansey ------ Center ----- Area 2 ----
Kangashkan --- Area 3 ----- Area 1 ----
Scyther [FR] -- Area 1 ----- Center ----
Pinsir [LG] ---- Area 1 ----- Center ----