I get them off the binary newsgroups. I don't know where they originate but they're probably off of a bootleg CD or maybe even the artist themselves are posting them. The text info for the van halen stuff says Tracks 1-10 were recorded live at the garage Oct. 1977.
Tracks 11-16 live at Pasadena Hilton 1976.
Tracks 17-25 are all Eddie solo studio recordings. In the studio section theres two versions of Eruption and the rest are the guitar tracks alone from the first album.
Somebody must have had access to the original masters at some point and copied them. I've seen alot of this kind of thing lately in the newsgroups where theres alternate mixes of 70's and 80's tunes or demos done before the album was cut. Theres tons of Beatles, Rush, Led Zepplin and Rolling Stones stuff too.