I took apart a car door mirror to free up the spring loading. I found it was all rusted up, so had to butcher it. The spring is held captive by a fixing I have seen before, but can't think of the name, to order replacements....
It is commonly used to retain a spindle by pushing it onto the end. It looks like a domed washer, with the internal hole cut outwards radially a number ot times, so creating tines. As it is pushed over a spindle (in this case) the tines drop into a groove, under slight spring, so preventing it going back the other way.
If it still can't be identified, I will take a picture of the butchered one.