Hi Martin,
There is no manufacturer’s p/n listed against 6A/942 but there are the following manufacturer’s listed for spares for the Mk1B* RoC, they are: Kelvin,Bottomley and Baird: Korrect Depth Gauge Co and Smith’s Aircraft Instruments Ltd.

The spares listed are mainly bezels and glasses with more listed for the Smiths item than the others.

The info is taken from AP1086 Vocabulary of RAF Equipment, Book 7 Section 6A, Aircraft engine and flying instruments, accessories and unit servicing spares dated 1950. Another copy of section 6A I have dated 1966 does not list the item.

Regards
Dave