There's been some discussion about sequential shifters of late.
I've made a few enquiries and here are some of the available products:

(1) Ikeya...made in Japan, available in Aust for around $2900 AUD +GST...possibly could be sourced cheaper ex Japan or US, but remember freight, duty, GST etc...6 speed and 5 speed

(2) K.A.S.S. ...available from Conquest Engineering in NZ...price into Aust is around $2500 AUD...5 speed only

(3) KAPS.... made in Czech Republic but have just set up a distributorship in Aust. Not cheap but appears to be the Rolls Royce product (used by many rallycross teams eg Travis Pastrana, Colin McRae)...around $4900 AUD...5 speed and 6 speed

For those who want to go OTT, there is also a company in the UK (Magnaparva) which makes WRC style paddle shift operated systems using single or dual paddles or buttons.

Steve, for 6 speed or 5 or both ?

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MY93 Impreza GX 1.8L, 0hp, 0nm

EDIT: The K.A.S.S. only do 5 speed at the moment. The other two do 5 and 6 speed versions.