You can buy them directly from Clark and Williams, though they're pricey. Oddly enough, it's a heck of a lot easier to get quartersawn cherry in 12/4 or 16/4, though potentially more expensive. Cherry, by the way, frequently shows up as antique planes made by craftsmen of the late 18th and early 19th centuries before Auburn tool, Sandusky, and other big factories made them so cheap that it didn't make sense to make your own.