Do you remember which pressure points you learned first, and which ones were the simplest?
The ones that I learn first where the ones we used the most: LI10, Lu5, TW12, St5, St6, St9, & GB20. You especially remember the ones you get knocked-out with.
When I think about learning pressure points (I know nothing yet) I imagine it being extremely difficult to get into them and practice them.
The problem is not getting at them, the problem is knowing the correct angle & direction.
I know that there is Dim Mak, but MA schools in my area are sparse and I don't expect to find a rare art.
Many arts incorporate PPs. Usually PPs are not taught as a separate art, and can be added to any style. Look for Kyusho-jitsu (striking PPs) or tuite-jitsu (grappling PPs).