Good luck with that Phil. You may be lucky with the couple of really knowledgable specialists in the UK. However if as Beans says, those pumps are not circulating in Europe, it may be harder than here.
It is not that spacers are not available, but with so few parts shop people knowing today what a mechanical fuel pump looks like, getting an assistant who knows how & where to find them may be very hard.
Try old fashioned tractor people, they use the pumps, & some actually have repair kits for them. I found the kit for my 40s Fordson Major fitted the spare pump off the 7.
However when My mate restoring a Dolly Sprint, & I both needed a spacer each, we tried all the usual places with no luck. The local triumph guru, Greg Tunstal in Brisbane knew all about them, but had none, & couldn't find them.
It was only when I was being told by a counter bloke at the local Repco parts shop that he had never heard of them that I got lucky. An old hand out the back heard the discussion, came out to the counter, pulled out the right parts book, [not computer listing], found 2 sizes available, & ordered them for me that we found them. They were very cheap once found.
I don't think you could print one. A thermo plastic would creep, & slowly squash under heat & bolt pressure. The things are made From a thermo set, [Phenolic or Melamine]. If you could find a suitable sheet of either, you could cut one out. If you are pig headed enough you could cut one out of aluminium, or if rich enough, get one machined from it.
Unfortunately we've had a total change of staff at the local Repco, or I'd offer to get one for you. I doubt the current lot would know.
If all else fails, try making one out of a sheet of ABS plastic. You could machine it with wood router equipment, & it could stand up for some years in that cold climate.
As I said, good luck.