I'm in Calgary, and have been following this and other diy fora since april. The Parkland Plastics product sounds ideal, but I've not been able to locate it anywhere here.
As an alternative, I visited some plastics distributors here in Calgary, and found that General Electric has a plastics division, and after giving them a description of the Poly-Wall (be specific!), they pointed me to a material called High-Impact Styrene. It has properties very similar to the polywall, although neither side can truly be considered "matte" finished. Both sides are in the semi-gloss range. However, I've mounted it onto a frame of 1x4s, and it's behaving nicely.
No hot spot from my 600 watt overhead projector, even without the lcd panel on top.
the 4x8 sheet cost $19, and rolled up enough to take home in the back seat of the Saturn. I realize it's probalby less perfect than the Parkland Poly-Wall, but I saved a higher cost, exchange, shipping and the time to get it here, plus the risk of damage in transit. Worth it, if you ask me.
You can see a pic of my screen (although it's not much to look at: a big white rectangle), in this thread:http://www.diyaudio.com/forums/showt...5055#post35055
Plus, there's a post several pages furhter back in that forum by a poster names "undream" who has pix of his construction, which I've blatently copied and used.
Hope this helps.