Other than the masterball try using a lot of ultra balls.
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The pokemon Suicune can be found on Route 25 of the Johto Region. If the pokemon faints or runs away during battle, it is possible to have a rematch at the Burned Tower in Ecruteak City.
The Shiny Suicune was a game stop event held before Pokemon black and whiter where releases. You had to get either suicune riakou or entei at the event of your Pokemon Pearl/diamond/platinum/soul silver/ or heart gold version, and then transfer them to your Pokemon black/white version.
after you have defeated all 16 gyms go to were you found misty and his boy and suicune will be there.
Catch a bunch of luvdisc they can hold heart scale.
Spinarak is a Heart Gold Pokemon not a Soul Silver Pokemon, You'll have to trade it.