Hi Tim
Those backing plates and plastic clips are the Siem ones. I have 3 spare clips you are welcome to which were gifted to me by Guy.
The problem you will most likely find is that the Siem style mounted lights are almost impossible to find. You can find the odd one, but I never found a complete set for my HPE and as such I had them re-silvered at not an inconsiderable cost as they were re-usable, most however are not. You will also need the stainless rings and plastic inserts for them which again may be an adventure to find.
Personally if you do not need the auto headlight adjustment found on the HPE and Saloon then I would switch to the Carello setup which is so much easier to fit modern lights to.
If you are after a set of backing plates and bowls etc, then I may know a guy who still has a pair I sold him and he never used from memory. also the various Coupes breaking may have Carellos, though I guess they may have the single combined unit which is different again.
Peter