Warning: I may know a bit about the stove stuff below but there is more that I don't know. Consider everything below to be a starting point for your own research. And pay attention to all the safety warnings you come across.
Earlier I wrote:
Gas fuel canisters come in two types: threaded, self-sealing and non-threaded self-sealing.
Those canisters come with a collar on top and a stem in middle. But you are likely also to come across a third type, a non-sealing canister with a smooth top that gets punctured. By non-sealing I mean that once punctured by the stove the canister and the stove cannot be separated (safely) until the canister is empty. The ones that are self-sealing can be separated and the gas remains in the canister. This can be useful when hiking because space considerations and also because if the gas control value on the stove gets turned on accidentally the stove and canister are not connected you don't lose the fuel or set anything ablaze.
Here are pictures showing the tops of these three canisters:
sealing threaded:
sealing non-threaded:
non-sealing:
I think Jetboil stoves are typically of the type that screw unto the threaded canisters.
I've read that the threaded types are the most common worldwide (there are many brands) but that the non-threaded types are the most common ones in France (it appears to me with my limited research that these are mostly sold under the CampinGaz brand.) Some stoves, like MSR's Superfly, can attach to both these types. You can get an adapter that will allow a stove that normally screws into threaded canisters to attach to a non-threaded canister. Here is a picture of one:
[ Edit: The converter could be discarded to save weight if it turns out that you can easily get the threaded canisters in Spain. ]
CampinGaz also distributes canisters of the type that are punctured and it seems that they may be easy to find thoughout Europe. They are cheaper than the self-sealing canisters. A few websites have cautioned that there are safety issues with these. The Kovea/Edelrid converter that
@homebuilt mentioned and linked to above will allow a connection between this kind of canister to a threaded stove. Here are those links again:
https://www.ultralightoutdoorgear.c...-technologies-puncture-cartridge-adaptor-p390
http://kovea.com/product/p-adaptor/
http://www.lusuh.com.my/padaptor-kovea-1004
[ Edit: The youtube id of the above video is pptkpueB_PQ ]
And here is a picture of a similar converter:
The initial comment/description on the youtube webpage points us to another webpage with written information for the converter:
http://weekend-adventurer.blogspot.com/2014/12/puncture-canister-adapter-edelrid.html
All these canisters may come in different sizes. For connections to the collared, self-sealing types there should be no connection problem but some canisters may be too tall to have a stable platform for cooking. The puncture type of canisters may also come in different sizes but as you can see in the illustrations the converter will only fit one size of these.
I came upon a couple of other sites that are helpful.
Adventures in Stoving:
http://adventuresinstoving.blogspot.com/
At the above site I found this page to be particularly useful:
http://adventuresinstoving.blogspot.com/2012/01/gas-canisters-101.html
This webpage is specific to the Jetboil system and it shows how to convert other types of canisters to the Jetboil stove:
http://pedaldamnit.blogspot.com/2010/02/jetboil-personal-cooking-system-remote.html