Hide in a forest, wait for some wood to walk past and jump out at it with a chainsaw screaming your lungs out? That'd probably petrify a bit of wood...
-OR-
You could, as mentioned, try some local woods though I'd have thought the chances of finding some are slim. Maybe try some fossil shops and the like, they may be able to help by either providing you with some or at worst, telling you where you are likely to find some?