Is there some darknet search engine that you access over Tor and type whatever illegal thing you seek such as "child porn" or "stolen credit cards" or "heroin" or "money laundering" into and it points you to providers of those illegal goods and services reachable over some reasonably secure channel?
Or is it one of those things where someone already using a particular child porn or stolen card or money laundering or heroin selling site has to put you in contact with them?
facebookwkhpilnemxj7asaniu7vnjj.onion
where the "Facebook" part is there for convenience and may likely not be present for actual illegal addresses. As such, you probably won't be able to find a CP website unless you actively brute force the entire onion address space.
I don't know how the sharing actually happens, but I don't think a real search engine for the dark net exists. There are websites that try (Ahlia, I think?) but they are super limited in scope.
I suspect addresses for drugs and CP are shared person-to-person.
I've never personally seen or looked for any images like this, but if they weren't already proliferating online and widely available to criminals, why would we need to build an elaborate client-side scanning system to detect and report people who have copies of them?