I find lots of info on making them but where to buy them? I'm sure plenty of people sell them but maybe I don't know the keywords to find them?
"For those who are new to “Makaizou” ( 魔改造, “Devil Modification” literally), basically when someone modified a figure (e.g. PVC figure, gashapon/trading figure, GK…etc) by taking out the clothes, adding *important parts, or doing any erotic modification, it’s called “Makaizou”. In short, make a normal figure into a naked/ero figure = Makaizou."
are the best ones i know of