Mdina have new old stock 16mm master cylinders.
https://www.mdinaitalia.co.uk/grimeca-f ... -16mm.html
You'd have to check with Doug if his parts have the tapping for the microswitch, can't quite see in the picture, but it does looke like there is a slightly square looking protrusion in the casting which is the bit where which my K1 is drilled and tapped for the microswitch.
However, from the MOT inspection manual it is not an MOT requirement to have both a front and rear brake light switch on motorcycles made before 1st April 1986. And even motorycles made after this date are only required to have both switches if it was manufactured that way. So provided you have a rear switch, if you have an original front Grimeca master cylinder with no switch provision, then it is not a requirement to have a brake light switch on the front circuit. If there is a switch fitted it MUST operate, but if there is no provision for a switch I think you are ok.
If you fitted an aftermarket or modern master cylinder with no switch provision then it would be harder to argue that the bike was made that way.
Of course, it's a good safety feature to have a front brake light switch, so regardless of MOT requirements you may decide you want to find a solution for this. If drilling the master cylinder for a microswicth acting on the lever is not an option, then since there is not normally room at the master cylinder banjo end, a banjo pressure switch in a yoke mounted splitter would be neatest solution but as a stop-gap you could probbly fit one at the caliper end, although it would look a bit odd.
From
https://www.gov.uk/guidance/mot-inspect ... -equipment :
4.3.2. Switching
Motorcycles first used on or after 1 April 1986 must have a stop lamp that switch on from both brake controls. However, a small number of motorcycles first used from this date were approved with the stop lamp switching on by only one control. You should fail the stop lamp only if you are certain that it was originally manufactured to switch on from both controls.
All stop lamps should light up immediately when the brake is applied and switch off immediately the brake is released.
Additional stop lamps, over and above the mandatory requirements, must be tested. However, if there is doubt as to whether they are connected, the benefit of this doubt should be given.