thanks for the Lion Picture link and the welcome. I'll ask them if the can get me this foam pad.
I've been using a mat board sandwich with a vacuum press so far and will use that with the mechanical press as well. However, as far as I understand it, the rubber pad is there to even out the pressure while giving some slack to account for the slight unevenness of the plate and quite some rough bottom shell of the press. I thought of stacking a couple of layers of mat board into the bottom and give it a try.