I know of some that are freely available but are missing. Has anyone figured out how to get word to them?

They may well be hidden behind the paywall:

> That one was on the house. The ones I really disappear into, the ones I probably shouldn’t spend that long on but happily do, live in the Hidden Tab. Members only, three a week, and they never come out here.

A mere $10 a month and the creator can profit off other people’s images!