Making Memories used to have several magnetic stamps sets. Here is the base: Making Memories Magnetic Stamp Base Set
Here are the sets: Making memories magnetic stamps - TheFind
The theory was nice: take individual letters or words on rubber backing and mount them on a magnetic sheet instead of wooden blocks. Place them on a metal magnetic bar and stamp away...
However, there is too much room from the top & bottom of the letter/word to the magnetic bar. Even centering them, they moved and got skewed. Too bad, it was a nice idea.