Can’t purchase Gold flora hairpin

I’m in ng+++ on PC and I only need the hairpin to get “A Curious Collection” and complete the game achievements. I didn’t purchase the hairpin in my first playthrough but I did purchased them in the next 2. To my surprise, in my 4th playthrough (ng+++), after completing the man-in-stone questline, I can’t purchase the hairpin from the man-in-stone anymore. It shows the hairpin is sold out in the store. So I’m missing only 1 curio to complete the achievement. Anyone has the same problem?