mexican chocolate for mole
The Mexican chocolate that your recipe calls for is most likely the tablets that are used for hot chocolate. It is a relatively crude mildly sweetened chocolate (i.e. not smooth texture) with a strong cinamon addition. A tablet or two of a dark chocolate with added cinamon should work. A tablet of the bakers would also be an ok starting point. I don't know if you need to add any sugar. The chocolate adds color and some background complexity, without being obvious.
Mexican chocolate really has a unique flavor and texture, but in a pinch you can use these substitutes...
for baking, replace each ounce of Mexican chocolate with:
1 ounce semi-sweet chocolate + 1/2 teaspoon ground cinnamon + 1 drop almond extract
for mole, replace each ounce of Mexican chocolate with:
1 Tbsp cocoa powder + 1-1/2 tsp oil or butter + 1 tablespoon sugar + 1/2 teaspoon ground cinnamon + 1 drop almond extract