a/c vent parts cross reference

[lotuseffect]

Anyone know where the best place to get a replacement 'eyeball' air vent - the one that sits at about knee level on an 88-92 MY...and I think most other years also? I have tried one or two of the independents but they have no listing. It strikes me the vent is most likely sourced off some other model of 70-80's british car (of which there are still heaps in wreckers around NZ)...but which one?

Si