Hausbrot has Avena that they call Gruesa... large flake. I tend to disagree with that definition but it's pretty much the best I've found. I hate instant oatmeal at home, and I guess the "avena fina" is their version of that here... Hausbrot have both in 1/2 kg bags, in dieteticas you can buy it wholesale usually. In Natural Deli you can find a "variety" (ie 3 different brands, maybe) of Avena.
Don't even think about steelcut... I've never seen it here. If I'm underweight when I travel back from Canada I usually bring a couple of kilos of oatmeal!