Just a thought, you could use the S3 switch in its place , its a generic Lucas part that is still readily available . It was used in all sorts of British cars of the era . You may still have the wiring and Hazard flasher unit still in place to connect to. The attached is the fitting instructions for the generic kit including the wiring diagram, which together with the LR diagram one could match it all together. The wire colors should match .
The kit is listed by Rovers North https://www.roversnorth.com/parts/pl...tch_series_iii The switch is available on its own, usually for less cost , this is one in the UK but gives you the idea https://www.autoelectricalspares.co....itch-913-p.asp