@Sierra02 - Yes, American pork tenderloin can be used in your lomo de cerdo dish. I've made lots of Spanish dishes using both pork and beef tenderloin from my local supermarket. The seasonings and other ingredients in your recipe should give it that true authentic Spanish flavor.
Here's a recipe I've used many times that I always get rave reviews over. Brown a half pound pork tenderloin in three tablespoons of olive oil. Then add one sliced carrot and onion and cook until tender.
Then add four bay leaves, two chopped tomatoes, three minced garlic cloves, one teaspoon of black pepper and two sprigs of fresh rosemary. Cover the whole thing with water and simmer for one and a half hours.
Add two tablespoons of red wine vinegar the last ten or fifteen minutes of cooking, then remove all the ingredients from the pan, cover with the sauce and serve.