We produce the Rising Museum Boards in the standard sheet formats used by the framing industry, plus we also produce the extra-large 60"x104" size. Although not quite 22x30, some artists who like to work on Rising as a surface for their work will cut the 40x60 sheets in half.
Thanks! I'm considering using Museum Board as a backing for a sheet of 30x22 Stonehenge, the extra 2 inches on the Stonehenge require some calculations.