If you're looking for this kind of product, it's usually best to go to specialty milling places (small studios that will mill custom lumber - eg traditional beadboards etc - they often have unusual supplies) or a dedicated hardwood supplier ($$$). These options may or may not work/exist where you live, but around me I can source some specialty hardwoods and softwoods (eg tamarack[1]) that definitely aren't available at regular shops.

[1] https://en.wikipedia.org/wiki/Larix_laricina