Searching only B&W pictures

Please help me. I want to search into my whole hard disk ONLY the B&W photos scattered into hundreds of folders and subfolders. Don't know anything about metadata, but they are scans from old analogue pictures. Bridge can find only 5 B&W pictures but I know they are thousand! maybe those 5 are declared B&N into the file info, but I need the software to recognize the "absence of color" more than the file properites. please help!