It appears that El Molino was a brand name of yeast produced/marketed by the El Molino (flour) Mills company - they had a cookbook they published using their brand name products (like many other companies did and still do) - last published around 1983 - can't find any indiciation they are still in business.
Just use another brand of yeast - sure it will turn out just as good.
If the recipe calls for a "cake" or "cube" - that's fresh yeast - hard to find these days. You might want to check this Baking911 page for suitable yeast substitutions
Hope this helps!