lake of rage
you find a red gyrados at the rage lake
You have to catch or defeat the red GYARADOS
You can trade it from heart gold/ soul silver or get lucky and find a shiny magicarp (golden/yellow) and evolve it into shiny gyarados (red gyarados)
you aren't supposed to defeat the red gyarados, you're supposed to catch it
Talk to Mr.Pokemon after you get a red scale from the red gyarados
you don't get one.but you can in Pokemon gold,silver,heart gold,and soul silver.
no, only evolving a magikarp it will be blue
he is at the lake of rage after you encounter the red gyarados
at the lake of rage outside of mahogany town
After you fight the Red Gyarados at Lake Rage, go talk to Mr. Pokemon. He will offer you the EXP share for the Red Scale you get for beating/capturing the Red Gyarados.
yes, official immages show the red gyarados in the lake of rage and in battle
in a lake towards the top right of the johto map