To get Feebas you have to go to mount coronet to where you get a lake, surf on the lake and go to the top right corner. You then fish twice in the corner and then move along. Feebas will eventually appear but it may take a long time!
Hope this helps!
Pokemon Platinum Guider
it is found in mount coronet
Feebas are tricky to catch you can only find them in certain floors in Mt. cornet.
Mount corenet (the fog level)
i never saw the feebas till i got threw to sunny shore city
i think national is Omanyte and sinnoh is Feebas
you can't just find it you have to evolve a feebas signed:hartm017
mt.coronet
on the left of sunnyshore city. a fisherman has feebas
Yes inside the foggy bit.
mt coronet
fisher man
Feebas