Here are some mens!
Here is a playlist: (these songs were taken from that "AllMathers" channel.)
youtube.com/watch?v=XEXR8q7GTRc&list=PLC..
youtube.com/watch?v=9rclKR9XKYM&list=PL7..
youtube.com/watch?v=JBRKCrLN8tc&list=PLn..
I strongly recommend you to check John_Banana, a dope channel about leaked songs and you can find them in the highest quality, with artworks and some information as well.
youtube.com/c/JohnBanana/videos
Unofficial Slim Shady LP 2, this is made by fans and named "SSLP2", Eminem doesn't or didn't have a plan to do SSLP2 I believe.
youtube.com/watch?v=9iPzWw5ZW-4
Rock Bottom's Original Demo:
youtube.com/watch?v=FyRsibCdFcE
Bass boosted version:
youtube.com/watch?v=yVVBk4YBu4Q
Relapse 2, contains leaked songs when Eminem was recording Relapse.
youtu.be/8egNzlwHLks
King Mathers, this album is actually pretty known back in 2007, Eminem wanted to quit rap at that time. The description says "A 2007 fan-made mixtape of leaked songs from Eminem's hiatus. During this time period, Eminem was struggling with depression & writers block, causing him to want to quit rap. This is the unreleased mixtape he was working on, but scrapped after he went to rehab."
youtube.com/watch?v=5QyLSdyUwOQ
G.O.A.T. from King Mathers:
youtube.com/watch?v=hCzQz7g8O7g
Soul Intent mixtape: Contains "Fucking Backstabber", and "Biterphobia"
Soul Intent was a Detroit group, Eminem and Proof were in it.
youtube.com/watch?v=AdaG9fglnFQ
DJ Butter Fingers (a DJ from Detroit) was in Soul Intent, he released some unknown Eminem's Soul Intent tracks.
youtube.com/watch?v=3UaU9By9hsY&list=PLS..
youtube.com/channel/UC-K5nHvSrBTY-4d1zaL..
Fan-made "Eminem - 2003" album, contains some known songs like "Hail Mary", "Can I Bitch", "Bully" as well.
youtube.com/watch?v=dThrMTa1xYg
D12 - Dumpin: A song came out after Eminem released Infinite.
youtube.com/watch?v=HYeO0KSO9PI
There are many more on Youtube and Internet! For Proof (RIP!), sadly I don't know too much about Proof's underground/unreleased/demo music, but I'm pretty sure you can find some, and some of the links that I posted also contains Proof in some songs. Hope this helps!