Numis,
I do have one of these medals, cased, at home. I can take pictures if you are interested to see.
Consider that there were only about 1,600 Yugoslav volunteers in the Spanish Civil War, half of whom died during the conflict. Many more died thereafter, during WWII, fighting with Tito's partisans in Yugoslavia. On the other hand, many of those who survived raised to cover prominent positions in Socialist Yugoslavia, from being ambassadors, politicians, military leaders, etc. This makes any medal, document etc. of the Association of Yugoslav Spanish Fighters a rarity indeed.
In 1966 the Municipality of Zagreb, SR Croatia, decided to mark the 30th anniversary since the start of the war by issuing this nominal table medal to Spanish veterans - I am not sure if from the city of Zagreb only or broader. But I think about 100+ of these were struck overall.