I do think they have some of his work in archives in Hamanaka, but that's just Kato's art. For Lupin art in general it's scattered across many places. Right now you can go on Mandarake's auction website and bid on painted cels from Part 2 and Cagliostro. So some are circulating for sale, or in private collections. I mean I have a couple myself and I know other fans do too.
Some obviously is with TMS, but for this book, these sheets, they specifically said Otsuka was the one who gave them these pieces to scan. While he was alive he probably kept plenty but after he passed, who knows where all that art went to. I would guess a vast amount are long gone, lost, destroyed, damaged. Floods, earthquakes, etc damage buildings, paper is fragile and time can really age these things fast.
With a series this extensive and this old, there is no doubt that it's spread across many places. With Telecom closing now, more materials are sure to be scattered or thrown away just to save office space storage.
