I don't know, Lazur. If there's a market, it's probably not much of one. But I've seen such coloring books for sale in craft catalogs. So some people do pay for them. Check out the search link in the op.
"stock ime" If "ime" means "input method editor" which sounds something like Windows' Character Map, no, I'm not talking about that. (Although it's an interesting thought!) Society6, not quite that either, although that's closer. What's a spec site? I searched, no luck. Oh, you mean like printing computer graphics and selling it like art? No, not quite that.
I've been working on several drawings, to show what I'm talking about. That will be the next step, so people who have no idea what I'm talking about, at least have a clue. By myself, without making any major changes, the most I could do is offer them for download from IC. And of course I'll research where people buy these things already, to find out how much it would take to get involved (in that community).
Installilng some kind of store or shopping catalog software, is another option. I'm sure there must be at least one open source online store software. But just for selling this 1 item, it seems a little extreme. Just getting involved in PayPal sounds like a nightmare, to me.
However, someone mentioned having "Inkscape gear" for sale, either on the Inkscape website, or somewhere else (caps, mugs, t-shirts, etc.). And if that ever happens, that would be a great place to offer the coloring books. Another nice Inkscape product would be calendars!
Anyway, I'll have a few drawings finished soon.