hi angela,
I am not sure about blackboard paint but,
i was just at Jumbo last nite and i was looking at this blackboard sheet.(wall paper like, but probally thicker) It is re-usable. it is written in english too.

I do know that they also sell the MDF board there too.
I am not sure what the blk board paint is called in german, but i hope this helps you a bit.