Is there an expression along the lines of
Red cars, for the man, were like the birdwatcher's spatuletail
... assuming the spatuletail is a rare find for birdwatchers. I'm pretty sure I heard something like this not too long ago, but I can't remember what. It was definitely in that format - the profession and then something someone in the profession looks for, is unexpected to come across.
edit: I think I'm starting to recall that the expression was more along the lines of
the archaeologist's El Dorado
..or something similar, where it means a unique breakthrough or meaningful discovery of a field rather than an uncommon but still ordinary find.
Still though, I would like to know if there's an expression similar to the one in the first example.