Does anyone know where these are available from?

No known sources as yet, some talk of tooling for poly, or using generic adjustable link.

I couldn't find any bush, so I made this:

Good job, might try that myself. Presume you need a few other bits like sleeves for the axle side. Lets us know if it works and also how you adjusted it, manual mentions putting some weight in the back.

I deal with this place in Australia called Fulcrum suspension. They told me to bring it in and they would probably have some generic fitting part.
Kelvin - Brisbane.

Just bought front Bushes for 360 from http://www.fulcrumsuspensions.com.au/superpro.html. These guys make them and send them to Europe.

http://203.31.191.243/fulcrumCat/ for the online catalog