At 15:04 31 December 2015, Tony wrote:
With the FAA now OK with you strapping go-pros on your plane, as long as
they don't fall off of course, why on earth would you need a 337 to strao
a
mirror to a wing strut?

And with that in mind, here's a link to a sturdy clamp which has been
getting good field reviews, especially among the "off-road" airplane
community--Supercubs and such. It's intended for action cameras but it
looks like it would adapt easily to a mirror:

https://www.cloudbaseengineering.com/product/100-0002/

I have no experience with this product, nor connection to the company. The
other Cessna variant I've seen is using a couple of large gear (hose)
clamps to strap a truck mirror to a C-180 strut over felt padding. Not in
pilot's line-of-sight, but worked sorta OK.