Here in the San Francisco bay area and probably much of California, Trader Joe's carries Mahon and Manchego cheese.

The posts about Whole Foods are correct - they have an incredible assortment of Spanish cheese - Drunken Goat, Manchego, Mahon, Tetilla, Valdeon, etc. However, what Trader Joe's lacks in selection, they make up in price.

Also, Whole Foods carries Jamon Serrano. My favorite Spanish food: blood sausage. Where to find? Dean & DeLuca in St. Helena, the Napa Valley - it has a pretty long shelf life and is great in a soup with lentils!