If you can't find it, try gourmet places like the one on
Marienplatz.
If you're not in a hurry, I can also bring you some real honest-to-god argentinian Dulce de Leche (Havanna brand) back from Portugal after christmas.
My girlfriend lived in Argentina for a year, and I visited her for two months. We learned how to make Alfajores, acquired a taste for Yerba Mate, the works.
LMK if you find it, we might also want it in the future. As the other poster said, though, it's also easy to roll your own.