Boys and girls,
I've pretty much given up on my local places, as none seem to have what I need, or will only sell me a box of 100! I need a 12mm banjo union, with a couple of sealing washers. To then close the end of the fuel inlet, I need an M12 x 1.5 dome headed nut or similar. I may also need an M12 x 1.5 nut to take up any slack there may be. It only needs to hold 50 psi, so I don't need anything overly industrial.
Beer tokens await!

I ended up buying one off of this guy.. Ebay Link

It was a little pricier than I would have hoped, but was delivered quickly and I avoided spending ages searching local places.

If no-one comes forward with cheaper spare bits lying about, I may well order that tomorrow. Cheers.

Have you tried thinkautomotive?