convex mirror plate
TS5605's ancient mirror broke last year because I stupidly caught an elbow on it, and the *two* replacements I've bought since have both broken in the mounting, while the car has been parked up and nobody's been anywhere near it. Strange but true. The nut and bolt holding the clamp in place was not super-tight, so I don't think over-tightening can be blamed; cheap rubbish glass would seem to be a more likely culprit.
Most of the Glazing outfits I've spoken with deal solely with flat glass,
As suggested above by Charlie, I contacted Phoenix Wing Mirrors in Worthing, West Sussex. I spoke with Luke, one of the directors there. He made for me a new convex mirror of 3mm thickness, 135mm length and 44mm height, and having a convexity radius of 800mm.
The new mirror is about a millimetre thicker than the old one but all other dimensions including the convexity radius are a good match.
At the time of fitting, I'm happy with this mirror
Mirror maker: https://phoenixwingmirr