Magnetic Paint and Neodymium Magnets?

My guess, the magnetic paint is not effective, perhaps not even available. Long ago a company planned to market tin plated steel foil as a substitute for aluminum foil. If you can find some, you could put it on the wall with wall paper paste. Even the 3 mm magnets should hold the posters on the steel foil, but you may have to use about 12 magnets to hold a large poster reliably. Neil