Im looking for some older stuff with an underproduced, dirty sound to it like early Celtic Frost, Hellhammer, Sarcofago or Possessed. Thrashy but still with extreme metal overtones.
Concrete Sox
Hellbastard
From Ashes Rise
Audiopain
Sacrilege
Skaven
I also saw a website that was dedicated to South American metal bands and there was literally dozens of dirty thrash bands on it. Can't recall the name of the site, though.
Mutilator - Immortal Force
Pentagram (Chl) - Demo 1 and 2
Sauron - Thrash Assault
Torturer (Chl) - Oppressed by the Force
Slaughter Lord - Thrash 'til Death
Trench Hell - Southern Cross Ripper
Ok, not all necessarily 'old' in the late 80's early 90's sense, but they might as well be.