There are martial arts stores all over, and probably some local to you. Japanese bow are a little specialized though so you would have difficulty locating one on your own; better idea to find a qualified instructor anyways
I've seen several online stores, but can't make a recommendation since I haven't ordered any budo supplies online.
When I shopped at physical martial arts shops in Tokyo, some sold supplies for a broad range of arts and some specialized in kendo and iaido. I learned kyudo for a year, and the only place where I ever saw kyudo equipment sold was at a kyudo shop.