I bought a pair yesterday, £12, as spares, off-the-shelf in Aberdeen, from Screwfix. Mini-ball valves, 8 mm pipe size. The union nuts are compatible with some variants of fuel pipe nipple, although the OE Vin ones fit straight on to the body.
I can mail a pair to you, but not for a month, for we're off to La Belle France tomorrow. I don't suppose you're invading Europe again this year? We'll be at the French and the Italian.
(The first ones I bought were 1/4" BSPT (taper) male up, 1/4" BSP female down, so I used a male-male cross-over at the bottom. The BSPT isn't a problem. These most recent buys are 1/4" BSP (no T) male both ends. Use the link further down this thread to see them. You will also need Loctite Hydraulic seal, which is good stuff to have anyway. Apparently someone on EBay sells ex military stuff that's past its sell-by date at 1/10 the price of new, and since in my experience the stuff remains effective for up to 25 years, it's a good buy. You need grade 542.)
Let me know.