Hubbard's 'Excalibur', as far as I know, is not available anywhere. Gerry Armstrong read it in the late '70s, early '80s ("2 1/2 versions"), as did some others around the time it was written in the late '30s. (Google is your friend).
Filbert's 'Excalibur Revisited' had its title based on the incorrect assumption that Hubbard's 1938 unpublished manuscript 'Excalibur' contained, in condensed form, all of what later became the Scientology "Bridge."
Additionally, Filbert was supposed to have taken this off the 'Akashic records', just as Hubbard was supposed to have done (according to Filbert) after (according to Hubbard) he "died on an operating table." According to his diary, later revealed, Hubbard had a Nitrous Oxide experience at the dentist, after which he wrote 'Excalibur', a psychology & philosophy centered around the idea of "Survive!", through which he hoped to "smash" his name into history. Hubbard's 'Excalibur' does not seem to have been "spiritual" in nature, having more in common with Nietzsche and Mussolini than with Buddha.
http://forum.exscn.net/showpost.php?p=100417&postcount=47
I had a paper copy of Filbert's 'Excalibur' when it was first being circulated around, many years ago. It was exciting and new then. Now it seems kind of silly. Those recently out of the "Church" of Scientology, but still under the influence of the "Scientology Bridge," have been known to become mesmerized by it. It's mostly regurgitated Scientology "Bridge" with an ample helping of Filbert's opining.
It buys completely into Hubbard's cosmology, with implants and BTs galore. Those still under the spell of the Hubbard "Upper Bridge" will probably find it agreeable.
http://www.forum.exscn.net/showpost.php?p=245719&postcount=14
A sample of Filbert's version of OT 2, demonstrating the solvent/lacquer mix (truths/off-the-wall significance combination) that Hubbard had perfected by the early 1970s:
http://freezoneamerica.com/Prometheus04/otTwo/preot2/filbert.htm
'Excalibur Revisited':
http://www.freezoneamerica.org/excal/excal00.html