You can catch him at the top right corner piece of land in Kanto,
See related link below for the Kanto map.
It has a dead end in the top right corner, that's where suicune is, but you have to find him everywhere else in Kanto and Johto region.
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Where you find Misty.
You can catch Suicune at Kanto Route 25. If you run away or Suicune faints you can have a rematch at the Burned Tower.
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Suicune is at Level 40 in HeartGold and SoulSilver.
chase it then you can catch it find out where it goes on seribi.net
On Cerulean Cape
LVL 50
there isn't a wild suicune to catch in white or black
after that, someone at the battle frontier will tell you about latias and latios. then, latias will start roaming kanto.
Ho-Oh Lugia Suicune Articuno Zapdos Moltres Mewtwo Kyogre Raikou Entei Latias
one and one only