If you DIY types purchase some vintage test equipment and it doesn't come with a manual, you can try looking here:
http://www.logsa.army.mil/etms/welcom1.htm . This is the US Army site containing PDF versions of declassified technical manuals. I purchased a vintage HP 334A distortion analyzer and was in dire need of a manual. Plenty for sale on eBay if you want to spend $7 or $10. The ones being sold on eBay are the same files provided by the US Government. I also found the manuals for my HP 400E AC Voltmeter.
I added this to the links page for future reference if you happen to purchase some test gear and need documentation.
Mike G.
