A new one (if they are still available) will cost megabucks. A decent secondhand one will be very hard to find. Have you thought of recovering yours?
I did this myself and quite cheaply too!
1/ first find a source of soft leather. I bought a black leather mini skirt from a car boot sale for a fiver

Embarrassing I know, but don't forget you're going to cut it up - NOT WEAR IT! (unless that floats your boat)
2/ Remove gearknob from car and carefully prise the plastic shift position legend from its recess.
3/ Using a scalpel, cut the stitching away from one section. You can now carefully peel the cover from the metal gearknob.
4/ You'll now see that the gearknob cover is made up of four identical leather sections. Cut the stitching away from the most intact section. This part will now become your pattern (I transferred the shape to a piece of card to make it easier to use). Make carefull note of how far the stitching goes up to on the fattest part of the gearknob.
6/ Take off...SORRY, find your recently aquired foxy black miniskirt and using your pattern, cut four sections out of it.
7/ Either take to wife for stitching or do it yourself, but remember it needs to be stitched 'outside in'. Once you've done this, turn it inside out and stretch it over the bare gearknob.
8/ Depending on the fit, you may decide it needs to be glued down. If you have to do this, use contact adhesive only on the thinner section of the knob and the top where the gate positions go. Slide the cover on while the adhesive is wet. If you do it once it's dry you'll never manage to slide the cover on!
9/ Looks ok? now stick the gate legend back on and return gearknob to car.
I really ought to get a job on 'Blue Peter'.....
Terry