I don't have the specific gauge of pop rivet you would need, but if you could take some of the drilled out rivets to Lowes, I'm sure you could match them up. All you would need then is a pop rivet gun.
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Alright, I'd grab the kit above or something comparable if you can find it locally. That way you have an assortment of rivets and a gun. Pop rivet guns are badass, and everyone should have one.
Not sure about size since I replace all the rivets on mine, my wife's and my daughter's case with 4-40 machine screws. My daughter's case was an Antec 900 and the rivets were no different than what you find in most any case.