You can get that same kind of mirror but probably larger and convex giving a wide field of view, from various marine outlets, used when pulling waterskiers. They may be too large for these cars tho.

I’ve got something very much like the original tiny “desmo” mirror and have not found it inadequate. I suppose any of the big “panoramic” clip-on mirrors would slide over it for all-out race use though. And with my car’s performance, I’d see a lot of up-and-comers in it.:-)

I’m with Dan. I have a simple “two-screw” cowl mounted mirror, and replaced both fender mirrors with convex mirrors in teh original style. I can see fine.

And if that mirror does not give you a sight line through the rear window or over your folded roof, you might be able to adapt the slider rod style (same mirror with a different mount):

Greg, I hear you about surprises from the rear.  I bought a brand new dash mounted mirror from MG Magic.  Exactly like the old grungy one that I had on the car.  Amazing what a difference it made in brightness and clarity and now I can see (to the rear) much better.