Salander also buys all her furniture at Ikea. But Ikea doesn't sell Billy's Pan Pizzas at all. Ikea sells Ikea-branded foods and none of this Billy's Pan Pizza.
Since we know Ikea is a real place, it's reasonable to conclude that Billy's Pan Pizza is a real food item, too. The Internet reports that it's not a high-quality frozen pizza, but given the noteriety it has from these three books, soon to be Major Hollywood Motion Pictures, when will Billy's Pan Pizzas become available for all of us in America?
I am saddened that the local Ikea doesn't sell them. But I can drown my sorrows in 50-cent hot dogs and meatballs with ligonberries, which are pretty decent consolation prizes, I guess.