I find the Savoie’s Smoked Green Onion Pork sausage at many Acadiana-area supermarkets, and you can buy it online at
Savoie's online shop but feel free to use any quality, smoked sausage. I found Creole red onions (a sweeter variety) at a local farmer’s market, but feel free to use traditional red (purple) onions or even sweet Vidalia onions.
Crab boil is readily available in Acadiana, but you can replace it with a ¼ cup of Cajun seasoning added to the water.