For example, I'm in a really small production of Romeo and Juliet and I want to look up information/history of Elizabethan Era swordfighting to better understand it, to better understand Tybalt, my character.

Thanks!

There isn't much that can't be found on the Web these days:

Elizabethan.org

You'd have to find some of these books in a library:

references to Elizabethan swordfighting

But some of these (fully readable on line) might have useful info:

fully readable refs to Elizabethan fencing

Start with google and go from there. You might even be able to find bits and pieces of the play on youtube.