I painted Cherry stabiliser housings the other day. I noticed that you can't have paint on the clips that hold the metal bars because then the bars won't clip and move properly. I will have to remove the paint there and maybe even paint the tops some more.
I masked off the internal shaft where the sliders go. I used Adhesion Promoter to get the grey primer to stick better.
I'm not going to bother to paint the black sliders.
Or a Cherry MX or MX-compatible Chicony 5181 or 5182 (the one shown is an Alps version, but the main part of the stabs is the same)
That one has blue clicky SMK switches, the ones often called "Monterey". Indeed they are compatible with Costar, but most of the ones on mine are already broken. Maybe cheap plastic.
I have also found grey Costar-style mounts on an Alps keyboard.