I can only think of the cartoon Costa where you can only find two 5 minute DVD rips of the german version online and some screenshots. Out of 100 episodes I couldnt even find one.
There is also supposedly a lost movie adaptation of the Alfred J Kwak TV Show from Nederlands which was supposed to be released somtime during the early 2010s but nothing was heard from it ever again.
—Paging Emma (Puerto Rican out of print movie from 1999, I personally really want to watch this film) —Nezahualcoyotl: la gran historia (meaning "Nezahualcoyotl: the great story"; Mexican animated movie. More rare than lost, they say it has been shown on schools.) —Toña, nacida virgen (meaning "Toña, born virgin. Extremely rare mexican movie.) —Michoacan (mexican documentary about Elena Sanchez Valenzuela from 1937)