There are some Lucas 722 wrecks on ebay at the moment that might provide the bits you need. They are in the 720 series which are essentially the same lamp but with a different finish black with bright parts, nickel finish etc. Other variations are body and base material steel or brass; base shape; door with security lip to hold in the vessel and finally fixing type fork or spade mounting.

Remember these lamps are handed and it is customary for the door to open inwards towards the vehicle.

Try this place, they restore lamps and do tool up some parts. I got a reflector retainer with red glass for the back of my king of the road lamp that was missing it. It's the part you can see from the back so that you can see it is still lit and it screws into the reflector.

https://www.geniusofthelamp.co.uk

As did my father.

Having cleared several estates now, it's not something that worries me.