If you are a tortilla fanatic like my partner Leslie Fenton is, you make your own.
If you are still pretty serious about tortillas, but not ready to make them from scratch, then you will buy the fresh corn tortillas found in the refrigerated section at a Latin grocery.
I also like the whole-wheat, soft tortillas but not so much the regular wheat and crunchy varieties.
Any slow-roasted beef or pork roast is a great candidate for a taco party. Season a roast aggressively, pierce with a sharp knife and fill the slits with garlic, sear in a hot pan, then place in a slow oven (300º F.) with 2-4 cups of water or stock and cook until falling apart.
Allow to cool, then pull apart and mix with the rich pan gravy. Top with salsa and avocado.