strictlymedicinalseeds.com is a great source for all kinds of
medicinal herbs. I just checked and they do have astragalus. They are also based in Oregon but I'm not sure that they are actually growing all of the seeds that they
sell (seems impossible when you look at their extensive catalogue) but if they are then they are oregon adapted astragalus. Otherwise I have no
experience with the plant, I have communicated with the company about other seeds from them before and they were happy to share tips about cultivating them