I've been through this same issue with the Nervar cranks on my UO8. They are 9mm, and as I recall, about the 3/4 style in Auchencrow's picture, not the one labeled Peugeot. I'd go into Harris and ask for cotters and they'd ask what bike and I'd say a UO8 and they'd give me something they called "French standard' but it was maybe 8 or 8.5mm and I'd find they don't fit and then take them back and they'd give me something else that would go too far into the hole. On the 3rd try they'd get it right but express amazement that that was the correct type.

The problem with filling them yourself, or I should say, filing them myself, is that I could never keep the angle consistent. If you don't, the cranks won't be parallel. Do note they are soft metal and file away quickly.