Caio Paolo,
If you are making your own model then we normally machine our cylinder liners. They can be made of cast Iron or in Aero engine models steel (EN8) is often used.
The term "segments" has not translated correctly into English: You have mentioned the red silicon O rings so do you mean the rings for the piston? We also turn those up ourselves out of cast Iron. In the UK some of the Model Engineering suppliers will supply them but in limited sizes. You should also be able to buy them in Italy. Think of small IC engines, like Lawnmower engines and see if you can find one with the right bore size.
If the Silicon o rings are not lasting very long it could be that the liner surface is still a little rough. Cast Iron rings "bed in", i.e. wear a little against the cylinder liner this makes the bore of the liner smoother. What this means is you need a better finish on the bore of your cylinder if you are going to use O rings.
Jo