For the inside track on the early history of Elektra you should read Jac's book Follow the Music: more info on the book web site.
Mick Houghton's book on the Holzman years of Elektra is called Becoming Elektra, published by Jawbone Press and with album sleeves courtesy of this discography ... highly recommended for all Elektraphiles. This latter has two editions, the first with more images and a second revised edition with extra chapters.
There is an extensive listing of Elektra and its associated labels on Mike Callaghan's extensive Both Sides Now web site. Much of the early information there came from my discography for 'Follow the Music' but whereas I stop in 1973 the BSN listing continues.
Discogs may be a source of discs and you can search on Elektra there of course.
If you are interested in Nonesuch Records then here are links to Karl-Michael Schneider's listing and Discog's listing of Nonesuch albums. (These open in a new window.) The Discogs listing leads to track lists as well but it covers multiple versions of albums with multiple numbers so needs a bit of patience and interpretation.
... and, of course, there is the real Elektra Records web site.