Viewfinder for shooting on a 8X10

[Bill Poole]

If you have an iPhone, I recommend an app simply called Viewfinder. You can set the film format, focal length, and there’s even a rudimentary light meter (although I would never use it). You can also set custom film formats and focal lengths.

+1

[Oslolens]

If you have a 3D printer, there are files available for view finders.
This one has 60mm diameter, but unfortunately not available without buying a camera

https://www.ebay.co.uk/itm/333648330264?

[Robert Opheim]

After years I bought a very used linhof viewfinder. It is 4x5 format so the proportions are the same as 8x10 format. I convert the lens settings on the finder to the appropriate settings for 8x10. So 210mm on 4x5 works for 300mm on 8x10 (approximately). This saves some time in set up in the field. It also works for finding images.