Hi Martin, if you are looking for a good, museum/archival board, you'll have few choices, but if you need something simpler, like white-core etc, most art supply places have it, even the one in Wexford St not far from Gunn's. For the good stuff, I go to, or have it delivered, by Glenwood Mouldings in Newtownmountkennedy—ask for David Woods, 01-2011678. They sell Colourmount, and the Museum board comes in just two white colours, bright or soft, codes 202 or 204. For a 10-pack of 32x40" raw sheet you'll pay about €95-100, which is pretty good. They also sell single sheets.

As all raw sizes, you need to square and size them down, and you won't get 4 16x20 I'm afraid, there is just about 8mm variation in sheet-to-sheet size, and odd bumped corners, especially if it is delivered... I don't know anyone who could sell me 32x40 with perfect, undamaged, square corners, and exact dimensions. If you do, let me know, otherwise plan for some wastage.