It was possible to retrofit to the 1600 series, so i don't know why with a little ingenuity you couldn't do a 1460. I haven't a clue as to where you might look for a used one.
i'm from southeast Pa and we have a local Case-IH dealer that is very helpful and i'm sure would be able to hook you up with some kind of used yield monitor. The dealer is Hoober Inc, phone 18007320017. Ask for the combine dept. good luck
I am a dealer for Ag leader and can get you a YM2000, PF3000, Advantage, Insight, etc... I also have a used (like new) GPS unit if you are interested. If I can help you out, reply to me by e-mail.