I couldn't help but laugh at your post title and then you saying you have "regular" size ones. Ha Ha.
I have seen Paul Gertner's new lecture where he does this cups and balls routine. It is outstanding.
Not sure if you could buy steel ball bearings that large online or not. I wonder where people get them for pinball machines? That is who I would contact because the small ones he uses are about the size of pinball balls and then his final load is a really big one.
Whoops...just reread your post....you already have the regular ones. That last one is huge. Did you try just contacting him yourself? He is a really nice guy and I'm sure he would point you in the right direction.