I found two great materials at Tesco, they're not strictly Montessori but can easily be used in a Montessori way.
The first is a magnetic map of Europe, it comes with a set of magnetic flags and magnetic labels for all the countries and cities in Europe. Little-N loves working with this. I decided that I will introduce him to 5 flags at a time.
The second is a a squared magnetic board that comes with small magnetic number tiles. These can be used for Addition, subtraction, division and multiplication. Little-N will use this with the Montessori beads when he doesn't want to write. I was hoping that they would have magnetic numbers from 1 -100 [perfect for hundred board] but they didn't.