Theirs a fair few kits on eBay but how good they are I have no idea, also depends on whether you want to restrict the up/down, left/right or both motions.
I've seen people on other VAG forums fit newer OEM Audi TT short shifters to cars (I forget which they fitted it to... Golf or Fabia I think) but whether or not they'll fit out B6's I have no idea.