you don't
You can get him at the safari zone.
You can find Flaaffy's in route 42 and 43.
Houndour can be found in Route 7 in SoulSilver and it can also be found in the Safari Zone.
you can find it in the sarfaria zone
you cant find celebi in soulsilver
Hey I have growlithe in soulsilver get in GTS
yOU FIND IT ON WHIRL ISLANDS.
EVENT!
you can't
you cant find him
in the sinnoh region in Soulsilver.
saffari zone
in viridian city
Mahogany Gym
in the wild
in safari zone