Actually the number in Rik's VAOS list is for the standard "civy" type 3 position switch. I believe the 4 position switch came in a little later than that list. The number for the 4 position switch is MT3/LU/351590.
I still don't think the part number will help one iota in finding a switch though.
I suggest a shout in sales/wants section for a WD switch. Ron
Although not directly related to this thread it's worth noting that the replica switches are not in fact replicas, being made to suit Indian manufactured Royal Enfields...The operating cam form is different and thus the switch operation is different...If connected to a standard Lucas wiring set up they won't operate as intended...The cam can be removed and filed to a suitable profile to put it right though...Easy identifier for the 'replica' is that they are not marked LUCAS....Ian