Sorry it's taken so long to reply -- I've been a busy bee working 16-hour days getting ready for Turning Season.
A good profile is indeed essential for the canvas of these works. This one has an ogee shape with tiny foot. The inside curve is slightly undercut. (I'm sorry for the dreadful photo -- the lightened areas on the right and left are due to light reflection off the surface of the box).
And while I'm at it... I'll post a pic of the reverse as well: Crescent moon produced by turning, the star is pyrographized and gilded. (The writing just says "Halo" K. Kowalski, 2011).
To answer your question: I get most of my dyed plywood from Cousineau Wood Products: www.cousineauwoodproducts.com. (Contact Curtis Cabaniss email@example.com). They sell blocks, dowels, etc. I buy all of mine in full panels. (The product is called "Spectraply" -- non-resin-impregnated material.) They're very flexible on time and color, so you can order custom panels and have them delivered quickly.
Rutland Plywood also sells "Colorwood" -- ordering in panels can be cost-prohibitive, (I'm not sure if they still have a minimum or not), but there are retail outlets -- I think Craft Supplies, HUT products, and a few other places sell bottle stopper or rolling pin blanks... you may be able to ask them to cut a larger block for you.