When I was on my way back from Portsmouth yesterday & sitting in traffic, I saw...
Mazda 323f (these looked a good size)
Ford Puma (like Leet said - too small)
Renault Clio 02
Honda Accord 04 (maybe too small)
Toyota Celica 05 (think they stick out, rather than just a lense)
It's raining at the moment, but if it's nice tomorrow or Monday, I might pop down the scrapyard with a ruler and see if there are any of these or others.
I suppose they'll need the etched lines crossing down them like the existing ones, so it might prove difficult, but worth a try I guess!
Also, I've seen a lot of BMWs with front lights that could have caps that might be similar. Still seems a long shot though