The headache I think is that the car didn't leave the factory with them - they were a dealer fit accessory. This is the whole headlight assembly.
The unit as a whole is fine, it's just the larger dip/main beam unit that needs to be changed as the lens is cracked. However it appears that the size isn't a particularly common one for anything aside from motorcycles. Should have measured it while I had it out but forgot, from memory it's 5 1/2" diameter.
Annoyingly, nothing has any part number on it, the only number anywhere is stamped on the lens, which I assume is the Hella part number (992.981.01) which I have punched into Google without any success.
They weren't cheap when new, so I would really like to get them back on the car again. They do a far better job of lighting the road too (especially on main beam as you'd expect).
I've seen similar units on 106s and 206s in the past, but have never had the opportunity to measure them to see if they are the same size.