Dipstick
I'd get a telescoping magnetic stick that is also bendable...stick it in the oil drain hole and sweep the entire bottom of the oil pan. If you find nothing that its probably in the dipstick tube but cannot fall into the pan because its just sitting in the tube and touching the bottom of the pan. If you remove the dipstick tube it will fall into the pan as you remove it....then you're in trouble. But there's not really a choice here, you have to find that piece of metal.
I know someone though who refused to remove their oil pan when he dropped something into the pan......so he drilled a HUGE hole in the side of the pan so he can basically get anything out of it if it fell in....then he just threaded it and screwed a metal plug on with a big magnet welded to the outside of that metal plug, its been there for like 8 years.
I would drill the hole in the back and down at the bottom if I ever have to, then when the front end is up on ramps and I do an oil change I can use it to drain ALL the old oil out.
.


