I located an alternate, non-Triumph front brake master cylinder and rebuild kit. This is for the single disk bikes with 11mm front master size. I measured the Triumph and Honda bits, I am 99% sure these Honda kit will work on the Triumph unit. Below are pictures of the components and measured sizes. I used a Mitutoyo ABSOLUTE 500 series caliper, I literately trust this caliper with my life
This unit is manufactured by Nissin, same supplier as the original Triumph part. There are several external differences but the inner workings are the same. Fitting to bike was not an issue, the front brake lever looks like the original Triumph parts but is slightly different. I'm working on modifying the cheap chrome adjustable levers I have installed.
Honda part number for master assembly is 45510-MGF-305
Honda part number for rebuild kit is 45530-MN9-305
The rebuild kit is half the cost of the one sold by Triumph and readily available at my local Honda shop.
Honda on top, Triumph on bottom
Benefits to having the Honda unit, I can see the fluid level while bleeding the brake, rather than getting up and going around the bike to look. There is a small shield installed in the reservoir that keeps the fluid from squirting out while bleeding, no need to re-install the cover while bleeding. Very helpful!
Why did I go this route? My original unit was damaged beyond repair. All the correct ones I found for sale on eBay were damaged and pretty expensive. The used Honda unit with low miles and lever was very cheap (37$ shipped) and in great condition. I took a gamble and it seems to have paid off. The main take away here is that the Honda rebuild kit will work with the Triumph unit and it's half the cost of the Triumph rebuild kit.