I have an Indy with a ZX12 and the gear change mechanism bothers me, I'm thinking of switching to a control cable but unsure what size etc and whether that's a good option. It's not on paddles, just regular stick shift.

I tried using search but it seems to bring up everything today?

Mine uses 2 rods with adjustable connectors via a right angle lever above the gear lever on the engine.. Simples and works great.

Boat chandlers is your friend, throttle control cable, you can get many different lengths

Try this
http://www.locostbuilders.co.uk/viewthread.php?tid=35650

I have a couple of Fiat Coupe gear change cables in the garage - maybe too long for what you want but might be useful? I can measure them tomorrow!