I haven’t and I know the market is flooded at the moment. But if my book and FB group take off, I’ll probably ask people in the group to submit pages and curate them to produce as a coloring book. Author copies are usually only a few dollars, so you can give the contributors a free copy. People like being included in books, and you have a built in market within the group. But that all depends on how people respond. I’ll probably start the FB group sometime next month. I was hoping to have the book ready soon after, but the way it’s going… or not going, rather.