I'm sure new mahogany is listed but I'm equally sure there is no reason you can't use or flog on old timber otherwise 90% of the brown furniture in the world would be unsaleable. Good quality old mahogany, either "virgin" or recycled, is quite sought after by musical instrument makers among others. I spoke to a guitar maker a while ago about this and he told me they paid well for the good stuff. I've seen mahogany for sale by reputable dealers in recent years for woodworking - not something I'd choose myself for woodturning - very boring. I've got two or three sizeable beams (ex stair case parts) which I've had for 30+ years, and they were old when I got them, so if you find anyone interested in decent construction grade stuff let me know. Mighte be able to buy some new tools with the proceeds....