After our chat at Redfearns, an obvious thought struck me..
Why don't you just swap over the turret screw for the one on your windage turret?. If the thread's a bit foobar'd just locktite it in the windage turret, put the turret cover on and forget about it. It's not often you need to adjust your windage once set up and you don't need the screw to be a tight fit to turn the turret.
I'd be tempted to go down that route while you're searching for a replacement.
p.s. I know they're not as pretty as a Nick Murphy top turret, but my 3D printed direct replacement turrets work a treat. Just pop it on tighten it in place with the screw from your windage turret - job done.