I've recently built a 10x8 camera using very simple tools and materials (foamcore) and an Agfa 213mm f/9.25 process lens, sans shutter.
It's OK for the time being using a lens cap for a shutter, as my subject matter and use of paper negatives lend themselves to long exposures.
However, it would add flexibility to be able to work with shorter exposures.
I've experimented with making guillotine shutters, mounted in front of the lens, and they are adequate if rather clumsy. The diameter of both front and rear elements of the Agfa is in the region 75-80mm (3-3¼")
The best alternative my researches have thrown up would be a (used) Packard pneumatic shutter - behind the lens - but I have yet to see one for sale from the EU on eBay for instance, although of course they seem readily available from the US.
Does anyone know of LF or "vintage" specialists in the UK/EU worth contacting? I've checked Rockys (yes, I know they have a certain reputation) and Marriot, to no avail so far.