[BAracer]

Understood about keeping it original, that's why I thought I would ask.

I got out my calipers and measured the shaft accurately (rather than use an old pinion in my parts tray) and the shaft does come out as 2mm diameter, so that simplifies the options. I did find the Cartrix website after your prompt (I obviously didn't try hard enough before) and all the parts are available, although it seems there is a minimum spend before you can place an order to the UK. 

So I'm going to try the Mitoos M209 plastic pinions which, as you suggest, do look to be the same as the one on the car at the moment.

All good fun, and my Whitsun Trophy car ran for the first time this afternoon, so getting there!