There appears to be something related to John in April's issue of Vintage Guitar Magazine, who previously had a feature on him, with photographs and descriptions of many of his guitars back in 2009.
Here is how they describe it:
If you’re looking to expand your lick repertoire and/or teach your fingers some new things, check out Wolf Marshall’s “Fretprints” column in John Frusciante.
And, on this occasion, I would like to ask whoever gets it first to e-mail scans and/or transcript, as it will probably take 7-14 days for I-M.net's archive copy to make the trip from USA to Serbia. Thank you.