Hickok is still sorta in business, but a net acquaintance
says that they have absolutely none of the old manuals available
(not even archival stuff they could copy) and offers no support
at all.
You might try the following used/surplus test equipment manual
sites:
www.agtannenbaum.com
www.manualsplus.com
www.w7fg.com/manuals.txt
And off-Web, try,
Ed Matsuda
POB 390613
San Diego CA 92149
619-479-0225 (voice)
619-479-1670 (fax)
I have a feeling that a private manual owner may end up being
your best bet. You might also try posting on the Poptronix
site: www.gernsback.com
Best of luck.
Dean