In my post yesterday I overlooked one very useful source of commentaries and other books on biblical topics - Google Books.
From the search box on the Google Books' front page, you can type something like "Judges commentary" (without the quotation marks) or even just "Judges" and this will bring up pages and pages of commentaries. Many of them are the older out-of-copyright books, but you will often find more recent publications.
Click on one that looks promising, and then enter your keywords or phrases ("levite" and "concubine" for instance) in the search box half way down the page. In most cases this will provide you with several pages from the book that you can read. If not, go back and choose another commentary. (Not all books are fully searchable).
You could also enter your keywords straight into the front page search box, but this doesn't seem to work so well.