Having been reminded I had a couple of these somewhere, I also remembered that about a year ago I bought this stuff in sheets, and that vanished into the depths of my 'stuff', lol. Just been and found it out.
It was called 'Magic Stamp by Penscore'. Apparently its now just called ' Magic Stamp, and is actually made by Clearsnap.
Just did a Google search, and here it is: Magic Stamp
. They have it in sheets, and in single blocks, and you guys in the US get free shipping too!