Like "rosewood" the vast majority of "mahogany" used in instruments today does not come from endangered rainforests. There are many species of wood loosely called "mahogany" and "rosewood," and most of what's currently being used is from pretty sustainable sources.
Also, instrument building in general has a very, very minor impact on supply. Even if one counts all of the instruments being made of wood, from flutes to harps to guitars and ukes, the total hardwood used is a tiny fraction of what is consumed by the furniture and cabinetry industries. You could probably make thirty ukes from the hardwood used in one good dresser, for example. And, while we tend to get tunnel vision and think of musical instruments as a major consumption of resources, in reality there are far more expensive dressers and wardrobes made every year than fine instruments. I.e. there are far more pieces of furniture than instruments produced every year and each piece of furniture uses enough wood to make many instruments.
It's not hard to find good Koa because the uke builders used it all up, it's hard to find Koa because furniture and cabinet makers used it up!
Furthermore, wood consumption is no longer even the primary motivation that is causing deforestation (frankly, I'm not convinced it ever was). Most of the deforestation is caused by clearcutting for agricultural purposes - i.e. expanding cropland - in an attempt to feed a burgeoning population. Sure, it's easy, or used to be, to find places where loggers were hauling off entire hillsides of trees. Now, that is less common but deforestation hasn't slowed - it's just that now most of the wood either gets used locally for construction or is simply burned off. Is burning off the forests more environmentally sound than harvesting the wood? Probably not...
Now, I'm certainly not against being environmentally responsible, but I think
true environmental responsibility has to address industries in direct relation to their actual impact. It kind of reminds me of a Mad Magazine (is that even still published?) item thirty or forty years ago that showed a bunch of hippies demonstrating outside a power plant - then they piled in their VW flower busses and departed belching clouds of oil smoke... That wasn't just humor - it was actually a very accurate picture of the situation existing at that time - when that item was published the amount of airborn pollution from power plants was a tiny fraction of what was emitted by the millions of automobiles on the road. But, what did everybody want? Those dirty old power plants shut down. It wasn't until oil got really, really expensive in the 70's that we discovered that, hey, you can actually reduce pollution while increasing fuel economy - and thereby make a huge, huge impact on air pollution!
John