Borrow a new one?

You have to find somewhere to store it while it's in your possession, so that's a genuine, not counterfactual, use of the where-should-I-put-this algorithm. But you haven't wasted any money, and can give it back once you've fooled yourself into finding your old one.

It's an interesting thought, although I suspect that my where-should-I-put-it algorithm will turn out to behave noticeably differently when the item in question is borrowed, because the best place to put something does vary in response to that. (As a trivial example, a borrowed book should not be shelved in alphabetical order with the rest of my collection; instead it should go on a special pile of borrowed things, so that I'll remember that I have to give it back.)