For the uninitiated, the French have their own standard pretty much for every part of the bicycle, so no "normal" components will fit.
Approach with caution and pathological love for masochism.

I've bought frames from the following ebay sellers (both stock French stuff and rando framesets)

Both offer reasonable postage to the UK (a lot more reasonable than some UK sellers!).
First frame arrived very well packed & as described.
Second seller - frameset is in transit right now.
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Now I have to comment on this one thing; the French standards are normal, it is the rest of the world that didn't catch on. Important distinction. And we certainly don't want to offend them, not before we buy every last randonneur, porteur and camping bike from them.

Nice thread, I think more randonneurs and porteurs are a great addition to RB.
Yes that Barra heylet is nothing short of mechanical perfection. Few little details on that I might have to borrow! Racks and mudguards? Mais non!
* The small big print if you decide to embark on something like these.

As pointed out above, it's only around the late 80s and 90s France started to fall in-line with the common standards we all know.

Thankfully there are a lot of resources on St Sheldon Brown to help figure these French bikes out. At the time these types of bikes were very popular and quality level can vary considerably. Individual very small builders, bigger regional builders and the big names like Motobecane and Peugeot were all at it. There are lot's of brand choices.

The really bad news though. Weird standards are fine if there are enough replacement parts. Sadly this is NOT the case. Even despite the popularity, the parts supply is to the point of total depletion. The handful of original NOS parts are at an eye-watering price level because they are so rare. Used parts may have been used to death, broken, or incomplete. Virtually no one is making replacement parts to keep these bikes alive. Definitely proceed with caution - high risk of exploding the budget and an obscene amount of time looking for parts.

My advice would be to buy a complete bike if possible. Look for the tell tale signs of mileage, don't be too put off with dirt and grime.

The bottom bracket "problem" is not really a problem at the moment.
Just use the aftermarket cartridge bb cups with the right thread.

I imagine the cups should outlast several sealed BB units.

Also, Sheldon has a hack of running a JIS spindle in old French-threaded cup&cone cups.

The headset, as I recently found out, is an issue. Many older French frames require a very low stack headset (33-35mm not uncommon).
While Velo Orange make a French-threaded headset, the stack there is 41mm, as, I believe, is the case with some old French Campies. Chances are this won't fit the low stack frame.
Furthermore, French fork crowns come in 26.5 or 27.0 diameters, the latter requiring some fiddling about to find an acceptable race.
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