Just evolve a mareep
first you have to guse surf to go to a city and there is a phamacy there
secret potion which you get by surfing to cianwood starting from the beach in olivine
Go west of blackthorn city and in your party have the following Pokemon - Gyarados , Nidoking , dragonite and todile and capture it with a heavy ball
When amphy the ampharos is sick, she'll be at the top of the lighthouse in Olivine City. Surf to Cianwood City and get the Secretpotion from the pharmacy. Then beat the gym there and you'll obtain Hm fly, Fly back to olivine and go to the top of the lighthouse to give the potion to amphy.
Can't get amphy
You can't catch Amphy. Amphy is owned by Jasmine.
A house in Cianwood has a guy who give you a Secretpotion. Use it on ampharos.
You can not catch amphy
catch mareep, then evolve it into flaaffy, then evolve it into ampharos. amphy is ampharos.
in soul silver
You first have to talk to the gym leader that is on top of the light house in Olivine City, she will ask you to go and get medicine for the Ampharos(Amphy) that powers the lighthouse. Then you go and talk to the guy in the Cianwood to get the SecretPotion.
You must Surf to Cianwood from Olivine and get the medicine in one of the buildings. Then you must either Surf back to the Lighthouse or beat the Gym Leader, Chuck, and get HM Fly from the lady standing outside the Gym and Fly back to Olivine.