I would try VRSapples sheets. They look good, but you might struggle with alignment, because the whole plate will be magnetic. shouldn't be a problem if you cut into small squares.
I am on Version 3 or 4 at the minute
I found the magnets would pull off after time, and the alu sheets wouldn't hold to the plate. Finally figured out it was because the mask is curved. so on my last one i glued the alu strips on, then clamped it to the mask until the glue had gone off. This seems to have solved my problems now as my plate has a permanent curve, the same as the mask.