No such thing. It's actually not possible with the way the shifter mechanism is designed.
What's been done to mine is that the leaver has been cut down & a new thread cut on it.
This shortens the 'leverage' & makes the shifter 'feel' more direct.
(FWIW, if it was a 71C spec box (R32 Skyline, Silvia, etc.), then you can buy a short shifter it for one of those).