Hey Kendall,
If you go to Admin > Field Management and search for the hidden field that you are using to capture SFDC Campaign IDs, you should be able to see a list of all assets that are currently using that field.
At my company, we use Activity Source and as you can see from the screenshot, the forms that use that field are shown. You'll have to click on each asset to locate where they are (lots of back and forth, not ideal) or copy the whole expanded list and paste into Excel to audit. It would be great to export this list instead of having to copy it.