You probably want hog casings, and you will need a cure salt (Instacure#1 or Tenderquick) to add if you're going to smoke it. Morton's tenderquick should be available in the seasoning/spice section of your local grocery store, depending on where you live. Instacure#1 (sometimes called pink salt) you may find at a local butcher shop or grocery store, or you may have to order from a website.
Be advised that there are quite a few different seasoning blends that carry the "Legg's Old Plantation" label, and they all come in a puke-green bag. The one most commonly used in this area as a base, with some secret ingredient like red pepper flakes or whole mustard seed or CBP added to make it your own, is 'Pork Sausage Seasoning'.