I am also interested in 30x40 cm film for an English 12x15" camera. I don't know how standardised the sheets are/were for this oddball size, but assuming the prices are in line with film area I'd rather shave a few mm off a 30x40 mm sheet than cut down 12x20. I am also thinking of making an 11x14 reducing back for my camera, so European availability of sheets in that size is of interest for me.

I don't expect to be buying film in any quantitiy for six months or so, but I would warmly encourage any effort to get a European dealer organised.