i want a magickarp and was wondering how to catch it in white
First off, turn those answers into comments up there.
Go to Marvelous Bridge. A man will sell you one for 500. You must have room in your party.
Oh yea, welcome to the site.
you can only catch one by going to marvelous bridge and a guy at the beginning of the bridge he will give you a magickarp for $500 (make sure you have an empty space)