You can spalt your own wood Don. I found out by accident. I covered some fairly fresh cut birch in the attic of the shop on the place I had just moved to at the time. I used the planer shavings from the same boards to cover it thinking that might help it cure more evenly. I didn't know at the time that I had a leak in the roof above the pile and the shavings got wet. About 2 months later when I went to check the pile the birch boards were now spalted. You could probably do the same thing by spraying the boards with water and them covering them in Saran Wrap or plastic sheet to hold the water in. Spalting is the early stages of decay so you don't want it to go too long, just enough to get the effect. The fungus that is causing it dies once the board dries back out.
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.