To remove the knob it is not really a matter of force - more a case of finesse.
Grab the knob at the bottom, towards the back and pull back up and over the top of the stick - a little bit of jiggling also helps.
They are available aftermarket in leather woodgrain look and carbon fibre look that I know of - about $90, but IMHO the don't look real flash. The best I reckon is genuine - there is a hsv one - with logo, and I think a leather one from the statesman (?) that look schmick - dunno about cost\availability though.
If your knob looks cruddy cause it's used/abused - get a stock genuine one off ebay - about $30. I bought a complete selector unit and asked the guy to just post me the knob, and he only charged postage on the knob.