Wondering wrote: I did, thanks, but then I thought I'd ask here. Seemed too obvious and figured I missed it.
Yes, it's totally obvious but not implemented. It shouldn't be that difficult since it involves locating files outside of FCPX, not inside. Searching a media card would be a brute-force sequential search, but they usually aren't that big. For camera files copied to a hard drive, Spotlight indexing already exists. Apple's own developer documentation says: "You can help users access activities and items within your app by making your content searchable."
As a workaround you can drag/drop files from Finder to FCPX. Finder has very advanced indexed searching functions, including ability to search for video duration, bit rate, pixel width, pixel height, and codec. You can add those search terms to Finder by doing CMD+F, then in the left-hand drop-down box, pick "other". Any item you check will become a search term. You can also save complex searches, similar to an FCPX smart keyword collection.
See the tutorial "Complex File Searches Using the macOS Finder":