Thanks for the post, and welcome to the forum!
I'd forgotten about this thread, and actually have some now (big thanks to Scilly Suffolk for sending me a link) which I got for a reasonable price on
eBay. Just waiting for them to arrive.
I had seen those Spa ones, but I didn't really want to spend too much due to the nature of the project. At the time of posting all I could find on eBay in band-on was Campag shifters selling for anywhere between £50 to £150!