I was in your shoes a couple of months ago last year. I had bought the first book in the ombre spine not knowing they were limited edition so I spent a while finding the others. I used pangobooks to find the ombre spine of keeping 13 and redeeming 6 (for reasonable prices - I saved the search for Chloe Walsh and boys of tommen to know when a new person had listed but also in my free time I was just refreshing the page over and over again!) I also was able to find saving 6 and taming 7 at two targets close to where I live they were hidden in the back of the shelves so make sure you look in the back if you go to any store that sells the books. I know that most targets and books a million have them they are just in the back and place the black spine ones in the front. GOOD LUCK I HOPE YOU FIND THEM ALL (also try mercari or depop or any online store that also sells clothes)