The University of South Florida has scanned and OCR'ed at least 639 issues of the NSS News and made them available for download, as PDF's, on their website. It is very well done, nicely organized and searchable. There was a post on today's TAGnet saying:
http://guides.lib.usf.edu/content.php?pid=86148&sid=640893&search_terms=nss+news#
Click on "Browse" to see the issue covers (there's a "next" button to
peruse other issues). Click on "Advanced Search" to search (although I
haven't tried that yet). They also have about 15 issues of
"Speleodigest". These PDF's are apparently indexed by way of OCR.