Well..... I spoke to my father-in-law, who was probably the original source of this particular bag of crap, and he thinks it came from some old French doors, which I think makes sense.
I've tried googling around that though, and come up with nothing. TBH the lid for the duck house isn't all that complicated, so I'll probably just get some heavy duty T-hinges.
Watch this space for more "what the hell has Womble found in his shed?" posts though. Quite often I'll see in a Haynes Manual etc, "use a spring compressor", or "with a ball joint splitter"...... then I have to search google images to discover if I've already got one lying around that the previous people left. It turns out that usually I have, and just didn't know it. I think it goes with the username!