I might have something for you. Somewhere in all of my clutter I have a pair of very old after market knobs and I don't know what they fit but it might be that they fit Redfield being as that was what I was using long ago.
Take the cover off the elevation adjustment and take a pair of calipers and measure the inside diameter of the cover where the threads are and post it up. I will then do that to the knobs and we will see if they are close enough that they might work.
It'll have to wait. My caliper quit working on me...don't know what happened. I am waiting for another one, after 19 years of service... the thing just quit working...man that burns me!