TPMB12 - there are cycle shops everywhere in the Netherlands. Usually I would say in town centres though.
Ah, the thing with cycle shops in the Netherlands, is they are very much not created equal. You may well find loads of them, I can think of half a dozen or so withing 500m of my flat. But I wouldn't take my bike to any of them, as they would look at it and be confused. They are very much aimed at the Dutch BSO market, if you have a city bike with a sturmey archer hub, you'll be fine with such a shop. But your carbon steed? or a touring bike? Nah. In Amsterdam there are 4 bike shops I use, depending on what I'm looking for. One of them is my preferred shop for having work done on the bike, and that's a 30km round trip.
When you leave the big cities, most small towns and some large villages will have at least one bike shop, it will be in the centre somewhere usually, but it will have to cater to all markets, which means it mostly caters to city bikes, maybe some e bikes, and possibly touring bikes. Good bike shops are hard to come by.
But we digress. Back to the original question, you can get threaded canisters in France, whether you can get them where you are in France, or without a long detour to a decathlon or similar, is another matter. Camping gaz canisters are the most common, and if you can tolerate the extra weight/bulk, sticking an adaptor in your bag just eases the stress.
J