bulb cover

Hi again guys

Having just got my RRC hazard switch working again, as a result of a small piece of the red square warning bulb cover breaking off & preventing the switch from functioning, I want to replace the cover as aged plastic was probably the cause of the breakage.

There are complete switch/indicator units available (part # PRC5072) but does anyone know if the bulb cover is available new, or even the part number?
I have browsed the 'net but without success up to now.

Many thanks all.

LRcat says RTC5691
A quick google suggests finding somewhere that's got one is going to be the issue, a now sold ebay listing suggests it was also used on the Disco 1
www.ebay.co.uk/itm/375307573249