on emerald they are on route 119 there is an estimated 400 tiles but only 6 tiles is where feebas is he is very rare. and every time you change the dewford town "trendy phrase" it randomizes feebas tile location hope this helps you must fish with an old rod.
Miltioc
It exists in 4 random tiles that change every day. You must use the Super Rod. http://bulbapedia.bulbagarden.net/wiki/Mt._Coronet#Surfing_and_fishing
THE MOST ANNOYING POKEMON IN THE GAME In the route beetween foretree and mauvile, there is 5 or 3 i cant remember, squares that contain feebas out of 400+!!!!!!!!!!!!
There is no sacnner, so I don't know what you're talking about.