@matt.g.ward.esq came in with an excellent tip for niche finds… basically if you are looking for something rare and/or expensive enough you can retain a pro to find it. He recommended Danny Stewart at BassJapanDirect.
His prices look really reasonable to me and I could even picture myself using his services for something truly rare, because I really hate playing phone tag in Japanese. He ships overseas and in general looks to me like he is running a great business.