You just need to know how to search properly using "OS X" rather than "Mac"

http://www.synthtopia.com/content/2004/1...
http://www.amazon.com/iDrum-US27000-Virt...
http://www.apple.com/downloads/macosx/au...
http://www.freemacware.com/category/mac-...
http://www.zzounds.com/item--GLAIDRUM

That enough options for you?
Garage Band tutorial here
http://www.apple.com/ilife/tutorials/#ga...

Which version of Garage Band are you using?

I have Garage Band 03 and there are a whole heap of options for creating your own drum beats if you look in the right place...sometimes you just have to "actually" look

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