after beating Red, you can catch the three legendary birds: Articuno, Zapdos, and Moltres. You can also get the Red Orb from Professor Oak to catch Groudon in the cave near the Safari Zone. (If you show Oak Kyogre and Groudon you'll get the Jade Orb to catch Rayquaza.)
well u can catch the rest of the rares
You can always catch Groudon. And Rayquaza too.
you can not catch charzard in soul silver, but after you beat red, you can get charmander from pr. oak and evolve it in to charzard
After beating the 16th Gym leader, you can Catch Mewtwo, and then just train for Red.
'ZAPDOS' is found at the power plant, you do not have to beat RED but you will have had to beat the elite four for the second time.
just beat red then go to cerulean city then go to the cave
you find him at the power plant after you beat red, the power plant on route 10 all 8 kanto gym badges+you have to beat red.
If you mean how to consider yourself as beaten the kanto region in pokemon soulsilver, then you should find zapdos,moltres, and articuno. You should also beat Red (Ash Ketchum). Once you do that, you can catch Mewtwo.
I decided to do the no life thing and try to actually catch them all
He vanishes.
you cant catch kyogre in soul silver but you need red orb from mr Pokemon but you have to beat red first. oh you can catch groundon though in soulsilver
If you want to catch Mewtwo in Soulsilver , first , beat the elite four, then get all 8 badges in the Kanto region, then you beat red at the top of Mt. silver, after that fly to Cerulean city in kanto, go to route 24 and surf to the cave in cerulean. Deep in that cave is where you find mewtwo!