Pokémon Gold and Silver/Route 38-39

Trainers
When you fight Schoolboy Chad, make sure to grab his number - he'll tell you when Snubbull are swarming, and that's pretty much the only time you'll be able to catch one(except in Crystal, where it can be found on Route 34).

In Crystal, get Lass Dana's number after fighting her, and eventually she will give you a Thunderstone.

Pokémon found

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 * Snubbull encounter rate during swarms is much higher.

Items

 * Berry
 * Thunderstone - Given to the player by Lass Dana after defeating her in a rematch.

Route 39
There is a house with a farmer whose is sick, give it berries to make it healthier to get a reward, 3 makes it a little healthier, two more will make it a lot healthier and 2 more makes it completely healthy, (7 berries in total) then the Lady gives you TM13 (Snore)

Pokémon found

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Items
Mint Berry - Next to MooMoo Farm.

MooMoo Milk - For 500 at the farm.

TM13 (Snore) - From the farm owner for healing Miltank.

Nugget - Hidden between the Miltank.