On most tables in Oaxaca, diners will not find black pepper. This is because of all of the other peppers, chili peppers, that are used in the cuisine. It probably would be a waste to try to put black pepper over a dish that already has several different types of peppers. At the same time, it sometimes seems silly for salt to be on the table because much of the produce and meats are already salty; this is due, at least in part, to the disinfecting treatment used to prepare most fresh foods.
Also, after having been here for months I have realized mustard is a condiment that is also almost completely absent from the regular Oaxacan menu, unless a person is having a hot dog or hamburguesa or something such as mustard chicken at a fancy (and not typical Mexican food) restaurant.
I have a list of things it has been hard — or impossible — to find:
Russet potatoes, pickles, peppeoncinis, black olives that taste like home, and small curd cottage cheese.
Don’t get me wrong, Oaxaca has a ton of things I cannot find in US grocery stores. Chapulines, of course. And, chepil, a delicious herb made even more delicious in tamales. And, mandarin oranges that are are so sweet the sugar sticks to my fingers.