Hi Stefano,
For the cylinders/tubes, a little "trick" :
Do a search on Google with the word "tube" or "aluminium (or plastic) tube" or "pipe" then go to the related pictures, there You'll find a lot of pictures with metallic (or plastic) tubes, download the pics You like and, with Your paint program, cut and paste the section You want and change its colour and, if necessary the shape/perspective....
Examples :
Bookmarks