Potentially awkward given that it wasn't made clear whether a loan or a gift. But could you say 'Oh, have you still got that X that you had off me a few years ago?' and then if they say yes, you can say 'Well, I wasn't that clear about it, I know, but I meant it as a loan - it hasn't been a problem before but right now I really need it. Can I get it back from you? You can always borrow it again if you need it' (if that's true, which I assume it would be).
If they say 'no, we got rid' then I think you have to chalk this one up to experience.