Didnt get your PM yet, not sure if you can buy this one in a store, but you Could probably get something similar just not sure where ? if you want i can order one for you ?
If you have an Ace Harware try them. Mine carries them in different shapes, thickness and strengths (N50, 52 etc.)
I use a 4x1x1" block. It is really strong but can be a little dangerous. If you are bored try dropping these down a copper pipe Dont google the guy who lost his finger with 2 big magnets. The pics arent pretty. Sometimes they show up on google images when you look up these magnets.
The bigger ones can be pretty scary. Even smaller ones can remove some skin if you let them get away from ya.
you want something compact and strong ! carrying around a big bulky magnet To a coin show or around generally may get you in to a "sticky" situation..LOL