I find the people in Pixiv to be quite defensive about characters, items and clothes used in their renders. I think they don't want others duplicating their 'art' and selling it. I've only found one person to be open about assets used.
The police uniform product I saw had quite a few users, about 3 or 4 people, which seemed to indicate that it was sold somewhere. As for the Dilraba Dilmurat model product, I saw someone posting it as if they wanted to advertise and sell it, but they didn't respond to my comments or messages.