Spaz Stix Ultimate Mirror Chrome. Comes in a small spray can or a bottle for airbrush application. If the surface you spray this on is shiny glass smooth, you'll get a mirror finish. Takes several coats. Then when that's totally dray apply their special clear coat for the chrome paint.
It's made for spraying on the inside of clear lexan radio control car bodies. I used it on the inside of cast clear urethane emblems for old cars. Spray it on glass or smooth clear styrene and you have a mirror, both on the paint side and looking through the substrate.
Rustoleum has a similar paint, larger spray can, lower price. Also available in a "gold" color. But unlike the Spaz Stix paint the Rustoleum is only good for back side application on glass, urethane, probably lexan or polycarbonate. Its solvent carrier attacks styrene. The paint side stays dull - works exactly the opposite of any other "chrome" paint that has the paint side shiny but the substrate side dull.
What I'd try with the knobs is sand off any remaining "chrome" (it's actually vacuum vapor deposited aluminum) then spray the chrome areas with a sandable lacquer primer. Wet sand with several grits of paper. Finish with at least 2000 grit. Dry off then apply a second coat of primer. A kit of MicroMesh sheets should get it to a gloss finish.
Spaz Stix has white and black backing paint for their mirror chrome. White gives it a brighter look, black darkens it some, making it look more like nickel. Apply a coat of the backer paint and let dry. This can be difficult to get super smooth with the spray cans. Airbrush would probably work best, for the whole job. Know anyone with an airbrush?
Then you can spray on the mirror chrome, let that dry then the clear.
The key to applying clear over "chrome" or any other paint is the solvents. Some companies have clears with a solvent chemistry designed to not attack what's used in their other paints. Some use the same chemistry across their whole product line, which can make it difficult to impossible to spray one color or clear over another. Some brands have recommendations for minimum flash time between coats but if you wait more than X time you must wait Z much longer time before applying more.
For mixing brands, look for very different chemical names in the ingredient list. For example a xylene based paint may not attack a tolulene based paint or visa-versa. Clear lacquer can usually be sprayed over enamels, as long as the enamel has dried for plenty of time. Used to be that one could get all kinds of colors of lacquer in spray cans but now you're lucky if you can find anything but clear and primer.
Another paint to look at for chrome is ALSA. They have some great looking stuff but it's expensive. 'Course you get more paint for the money but for a couple of knobs three little cans from Spaz Stix for backer, chrome, and cleat coat will cost a lot less than just the chrome can from ALSA. 'Course you could go wild and do some chrome flames on your Ex with the ALSA paint while you're doing the radio knobs.
