Google "Tweaking glitch in 4th Gen". You can catch those two without getting the oaksletter or membercard if you can exploit that glitch. (Or atleast thats whats on Bulbapedia)
More on topic, best ball for
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I'm thinking Dive, since every shiny ralts I've seen is in a moon ball.
EDIT:
Here is a link: http://bulbapedia.bulbagarden.net/wiki/Tweaking
The Void Glitch is what is used to gain access to darkrai and Shaymin
They're still illegal because the card was never released for Diamond/Pearl.