Looked all over for exactly what size O-ring was best for dry firing my P01. There was plenty of information about some of the other CZs, but not the P01. So this time at home depot, I finally remembered to look at them. It's a pretty big selection, but common sense narrows it down to just a few.
I chose the #47 O-ring. 10 o-rings for $3 bucks and a perfect fit. If anyone is interested, I can provide the actual size of these. Just in case you're ordering off the internet, and not actually at HD.