The bulb holder is NLA, has been for some time.
You won't find a new one, but you might find a used on in the back of the heater controls of a RR Classic (same unit).
Or you can do what we do and use a bulb holder like the ones in your dash binnacle and drill a round hole in the dash (where the old one was square) and fit the new style holder and the stock green bulb RTC5605 (or somthing like that for the green bulb).
Works the same and won't snap like the older white brittle style.
I do not check PMs. Call or email if you need something.
ECR is not a parts source. We are not in the mail order business.