Pate (pah-tay) (I'm missing the accent mark over the 'e') is usually chicken livers, seasoned and herbed. Fois de Gras is duck or goose livers, seasoned and herbed. Southern France makes some of the best fois de gras in the world. Pate is the poorer man's fois de gras. I used to make my own pate or fois de gras for parties, or for when I wished to get my iron levels up (with some dry toast, first thing in the morning).
Try a search engine for either and your location. It used to be that many butcher shops carried pate as a specialty and I know it can still be purchased in most "special" deli sections of fancier big supermarkets.
Chicago has issued a "ban" on fois de gras -- "cruelty" to geese, yeknew. But the Chefs of Chicago are fighting back with a fury against the ban. How dare the Aldermen of Chicago dictate whom may eat what! I stand with the Chefs!
There is also a a man in Sebastopol, California who treats his geese very well and markets a fantastic fois de gras.
I lived in downtown Chicago, between Diversy and Fullerton on Lakeview, for 15 years until 1990. My wife and I used to eat at a restaraunt Ambria at the Belmont Hotel. One had to book a half year in advance to get a reservation. Best fois gras I ever ate. In Chicago. It was about $50 a portion way back then but boy, those geese were singing another tune.