im not sure but i know chromedaddyo sells some.{i think thats his name here}he makes them and im sure he can make any kind you want.
The gl*** swirl"onyx" knobs in red, blue, green. yellow, orange, and other colors hav ebeen reproduced since the 70s in round, round banded, and mushroom shapes. Try Snyder's in New Springfield OH. The genuine onyx and other stone knobs were reproduced in the 80s but I don't know about now. These were available in 4-5 shapes and sizes and were quite nice.
I seem 'em on ebay all the time..... search vintage shift, marble knob, gl*** shift, agate knob, swirl knob, etc. Good luck!
Wasn't someone here on the HAMB selling those really swirly gl*** ones? I can't remember the name of the company for anything!
dichrome x2, I got a shift knob and matching suicide knob (which I mounted on an old one that I bought off e-pay). They have a very kool selection of knobs to choose from.
Look at vintage doorknobs, cheap and plentiful in antique shops, flea markets, etc., can also be found on eBay--there are some really nice polished marble and granite ones, generally designed to fit on a 1/4" square shaft with a set screw, but can easily be drilled out and tapped for the threads on your shift lever.