Alternative front master cylinder

Try Holland Norton Works:

https://www.hollandnortonworks.eu/en/exclusive-commando-parts

Can't remember which model but it solved my wooden brake issue.
 

https://www.carpimoto.it/en-GB/Brand_Brembo/42207_10462095-Brembo-PS-13-Brake-Master-Cylinder.htm

or
https://www.carpimoto.com/en-GB/51016_10505351-Brembo-PS-13-Brake-Master-Cylinder.htm

but the remote reservoir might upset some people...

Same parts can be found in UK at higher price. Be sure to read CarpiMoto's terms for Britain post-Brexit.

A search at Aliexpress or Amazon might find you an usable Chinese one. Prised £10-20.
Last week urgently needed one for a (non Norton) classic racer. Fully functional, 3 days delivery, £20. If not what you wanted, probably you can sell it at an autojumble.

I'm rebuilding a Commando and I've used a Triumph master cylinder. They are available with 12 / 13 mm bore and with a stainless steel body. The hope is that it will give the bore size advantage and be more durable. The switch is integral with the banjo bolt and sourced separately and you need to have a special hose made with a banjo at the top. The lever is chrome rather than aluminium but the difference is not obvious and you can't fit a Norton lever. It took a bit of Googling to find the parts but it looks 'factory fit'. I've not run the bike yet. M/C was from E-bay, I think it's Harris and was cheaper than a stock Norton M/C, switch was from a company that supplies car parts (it works just fine, the pressure must be similar), hose was Goodridge, made at a Goodridge supplier that usually supplies parts for race cars, while you wait service. Hope that helps, can post a photo if you like? Best to bleed it all on the bench before you fit it.

# 13 mm front master needs 13mm unit.

OK = installed Andover Norton Triumph T140e unit 06.7163 from Classic Bikes - Standard 13mm unit fits direct onto existing Norton controls (1977).

Brake hose cover (elbow) from Triumph  T140e 60.4186

# Fit break sensor to new front master cylinder brake line.

OK = New kunifer and switch fitted between yoke’s (tree).