They don't seem to be advertised at the moment. I made some up last year. You will get Mini perspex visors on e-bay. These won't fit the Morgan but for about £40 you'll get the four brackets.

Then I had the perspex made up on line, laser cut and predrilled.

Example here: http://www.ebay.co.uk/itm/SUN-VISORS-BLACK-TINT-FOR-CLASSICS-AND-KIT-CARS-NEW-/151986635067

DaveW
'05 Red Roadster S1
'16 Yellow (Not the only) Narrow AR GDI Plus 4