Here's my two-cents (or less) worth on B-movie stuff.  Last semester I
saw on the cable station AMC a documentary about Republic studios.
I was loaded with clips, but I'm not exactly sure how to get a copy
(I assume contacting American Movie Classics would be a first step).
Also, I know that Susan Kray, a recent graduate of the Institute of
Communications Research at the University of Illinois, wrote her
dissertation on Republic.
Hope this helps.  Matt McAllister, Virginia Tech.