Try Lodima Archival Materials. We have ArtCare mat board--highest quality there is. We have the lowest prices anywhere. We have no minimums. And no pre-determined standard sizes, meaning a mat, say, 15.5 x 19.625 is the same for us as 16x20. Of course we have all of the standard sizes, too. And we are APUG sponsors.
We have added on to a building and will soon be installing a new guillotine. And we have a computerized mat cutter to cut overmats up to 40x60. And since we are photographers first who are extremely demanding with our own work, we can offer advice about anything to do with mounting and overmatting.
Right now we are preparing to travel for 6 weeks. Someone is here to handle orders, but it might take a few days longer than usual, but once we are back and with the guillotine set up we will generally fill orders within a day.
Michael A. Smith