if it keeps breaking on just the E I would check to see if there is a small burr in it first. Some carefull sanding might solve your problem without spending any cash.
The 'knife-edge' is nothing to do with the saddle. It's the part of the tremolo which rests on the bridge-posts (one each side) and acts as a pivot point.
You can get saddles from 'Ibanezrules' (swirly banner at the top of this page) but as Nightfiend said, you probably don't need one and could sort the problem out with the one you have.
Or try swapping the saddles for the high and low E strings. A small burr won't break a wound 42 so you might be good to go and its a free experiment. Just mark the saddle positions with a little masking tape so you don't have to re-intonate.
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