Roz ... try ringing the number on that business card I sent to you a while back, as they should stock it.
Alternatively any other art suppliers should do.
Ideally, Mark ought to go and take a look at the board Olly mentions to see what the surface is like on it ... it's suitability will very much depend on what medium you'll be using on it ~ pencil, indian ink, marker pen, pastels, gouache, watercolour and so on.
If you're still unsure ... then
ask!

Right ... my turn to shut up!
