How do I obtain a Spanish Card?

Under Spanish nationality law and the Historical Memory Law, your father was a Spanish citizen at birth, since his father was Spanish. This means that your father just needs to go to the nearest Spanish consulate/embassy and register as a citizen, providing he has documents proving that he is entitled to citizenship. This may or may not mean that you are also eligible for Spanish citizenship, depending on if they count your father's citizenship from the time he registered himself with them or from the time of his birth.

You can also apply for citizenship under the provisions set out by the Historical memory Act. If your grandparents emigrated due to political or economic reasons, the next 2 generations (your father and you) are eligible for citizenship. If you still don't qualify, since your grandfather was an original Spaniard, you only need a year of residence in Spain, before you can apply for citizenship (unlike the usual 10). If you STILL don't qualify, you only need 2 years of residence in Spain, before you can apply for citizenship, if you are a citizen of a country historically related to Spain (e.g. former colonies like Mexico)