Find...Usages

I am cleaning up an old project - a web app containing 900+ pages, a mix of .net and classic asp, a bunch of .css and .js files, images, etc.

Task: Identify which of the supporting files are not being used anywhere in the web app.

Example: questionable.js

Attempt 1: Find Usages.  No results.

Attempt 2: Find Usages Advanced w/ Textual Occurrances.  No results.

Attempt 3: Find Code Issues on the solution.  Nope.  If they are identified in there somewhere, I don't see it.

Attempt 4: text search Find In Files for "questionable.js" - Aha. There's 30 files using it in a <script> declaration.

Is there some way other than a bloody text search to find these?  If so, is there a way to do this in bulk?  I'd also like to check a bunch of supporting classic .asp files to see if they aren't being used in an <!--#include> declaration somewhere.  I'd also like to identify which image files are not being used.

Am I stuck with manual searching?