Ceeway have the brass adjusters, I assume these are the Kirk design ones. I have a parcel from Ceeway awaiting opening and there should be a couple of those inside.
I am still going to make some and see how they turn out. The current idea is a 5/16 UNF adjuster with the cable insertion almost right through. It sounds chunky but might look quite neat if I get it right. I will try 1/4 UNF as well but I dont think it will be strong enough with a 4mm hole almost right through. Just waiting for some stainless bolts to arrive before I can make something up.