Grab an extendable magnet off Amazon. Even if you get your knife back tonight these things are just too handy not to own. They make them for automotive work because dropping a bolt on top of the transmission is a pain in the ass.
could get a small telescoping magnet off amazon. something like or search for other options that are more suitable to your specific needs. Also, most hardware stores carry these telescoping magnets.
https://www.amazon.com/SE-8036TM-NEW-Telescoping-Magnetic-Capacity/dp/B000RB3XBA