If you can cope with vinyl (and are quick) there's a recording of he himself playing them up for grabs cheapish on Amazon.You also may find this interview interesting, though it doesn't relate specifically to the etudes, but it does have some tantalising looks at other pieces.I assume you know of his solo transcription of Stravinsky's Firebird and Rite of Spring, but he seems to have been quite prolific, though now much out of print.I have his Paganini Variations as part of my small collection of those, and a couple of other works. No leads on volume 2 of the etudes, though.
You also may find this interview interesting, though it doesn't relate specifically to the etudes, but it does have some tantalising looks at other pieces.