Colin Stamp wrote:

I need six compression springs, about 20-30mm long and fairly stiff,
to go over M5 screws. They're for some home-brew headlight aim
adjusters.

Looking online doesn't seem to be turning up anything suitable. I
guess I need someone that does model engineering supplies or something
like that, but a quick online search doesn't seem to be turning
anything up.

Did you try Screwfix? ISTR seeing a 'selection pack' of springs in
their catalogue.

David