Vitalis: it's just plain old mild steel gas welding rod. Again, I'm not sure how things would translate in your country, but phrases like "bog standard", "nothing special", "what most people use", possibly "low carbon", etc., should (after overcoming some skepticism) get you what you want. Note that in the US you wouldn't be able to walk away with less than a pound of rod -- if you just want one stick (probably a meter, if you're in a metric country) you may have better luck inquiring at a shop that actually does welding, rather than someplace that sells to welders.
Rod for TIG welding will work as well for our purposes -- it's pretty much the same thing as gas welding rod, but made to higher standards of purity. My local shop doesn't carry gas welding grade any more, because the TIG stuff is only a bit more expensive, it's what most people want (they look at you funny if you gas weld and aren't covered in wrinkles), and it works just fine for gas welding.