Who outside of the factory knows the truth, but here's a few more ideas.
Maybe they post stuff by demand. If there's a type of wood you want to use for a confirmed project, give them a call. Describe what you're looking for as best you can and maybe they can put up a few examples for you.
Maybe it's like a wine cellar. They have a bunch of wood there and it's all aging. There may be things you could drink now, but will be much better in another five years. All you can do is ask. Do you want something tonally exceptional in a particular style? Beautifully figured? Maybe a unique burl that goes beyond unique?
Also, I see koa on eBay and in other places periodically. The trees still exist and it is available. If Alembic doesn't have any right now, you could ask them well in advance to get you a piece on some future wood buying expedition. Either that, or talk to them about what they would want you to do if you hunted up your own wood and had it sent to them.