A Horsea will be found if you get a good rod and look for a lake or river.
Entei can be found in Nimbasa City in Pokemon Indigo.
Fish with good rod on route 226
Yes, there is every Pokemon on Indigo. The easiest way to find Pokemon is to go to the ROOMS.
I doubt you will find Giratina on Pokemon indigo as it is not a generation 1 Pokemon (it isn't one of the first 151 Pokemon species)
Go to route 226 and fish with good rod
NERD!
You find it in pokemon! it's obvious!
where to find a vulpix on pokemon UNOVARPG
anywhere
Find It In League Champion - Steven on the online Pokemon Indigo
You cant find it you can only get it as a starter pokemon.
You can find one in a room or pokemon locator