I'm afraid there isn't a straight answer to this question. The Martin D-40 has been built with Brazilian rosewood back and sides, Indian rosewood back and sides, and quilted mahogany back and sides. I've yet to hear of one with anything but a spruce top, and I hope I never hear of one with other than a spruce top, but it's highly likely there are D-40s with Adirondack, and also (most of them) with Sitka.
Because of all of this, I'd not at all be surprised to hear of a Martin D-40 with Koa back and sides. I've not seen or heard of it, but I wouldn't rule a Koa D-40 out of the possibilities of what is out there.
A lot of the D-40s have absolutely spectacular abalone inlay on the fingerboards. Production ran from 1997-2005. They came with Corian nut and Micarta saddle, but on something that nice, one should only ever be using bone, in my opinion.