Any clues on who? I've used tor to go search all the Japanese sites, and other sources I can find and still come up empty handed.
As far as I know this is how things work. I'll be honest, I have NO interest in getting into leaking myself, so some of this is speculation on my part.
-Providers get raw info/scans from early copies of Jump (outside of Japan, as Japan HEAVILY cracked down on piracy like that within the country).
-It's ridiculous dangerous for providers to leak shit directly, so they either give it to trusted sources, or, (most often) sell the info/raws to people
-The people who buy the raws/info then can either sell the information to others as well, or keep it for themselves to leak, or give it to others to leak
-In order to gain clout, leakers with direct sources will do a slow build up, releasing hints though others parties, and spreading breadcrumbs about some real and fake things in the chapter
-Some leakers like to add in more fake stuff than others. Despite his reputation, TAC does post reliable spoilers occasionally, but, since he loves trolling so much, he enjoys hiding the real stuff under mountains of ridiculous lies. It's why I love his "spoilers"
-People connected to people with direct sources will begin to leak bits of the chapter, trying to do it in a way where too much information doesn't come out too fast. The faster leaks comes out, the easier it is for the authorities to figure out where the leaks came from. This is why they are delayed, rather than dumped as soon as the leakers get them
-These people need to be trusted to not release information too fast, and too not reveal their sources
YOU ARE HERE
-Social media, and forums are spreading all kinds of information, mostly false. The more true information gets leaked, the more the leakers want to leak their own stuff, in order to get the clout for it.
-This is why, once you start to see some real spoilers come out, Redon/Lance will post a bigger summary of what happened, to get ahead of the other leaks.
-So, you also have people making fake spoilers, and post semi-real spoilers to bait out other spoilers. Example: Momo fights Green Bull. Rather than just say, Momo pushes Green Bull back a bit, but Green Bull is fine, instead, make it look like Momo did serious damage to Green Bull. Now, a leaker might correct that, and go, "No, Momo didn't low diff Green Bull, stop being ridiculous". This then proves that the Green Bull Momo leak was real to begin with.
The easiest way to get into leaking is be nice to people, be honest, and develop trusting relationships with people in the community. Don't try to get leaks from someone then post then behind their back. Be honest, and tell people you're interested in leaks. Most leakers are really nice as long as you're nice to them, from what I've seen.
I have no idea where to buy raws myself, and don't want to know, I have fun watching this weekly chaos develop. Hope some of that helps (once again, this is just from my experience listening to other people talk about leaks).