Back in the day, you could just ask for pork trimmings from the butcher. But now days, most cuts come pre-trimmed and cut in bulk boxes so there is less trimming (if any) for the butcher to do. Now if you have a local butcher that works in whole animal sections, they will likely have pork trimmings available.
There are other options though. Most grocery stores sell "fat back" or other pork fat in either flat sheets or cut into strips. It is not usually with the cuts of meat and in my local store is over by the refrigerated canned hams (you may have to ask for "fat back"). I hate paying for it though. Another source is to keep pork trimmings and freeze after vacuum packing. You want the good "pork back fat", not the soft mushy stuff from your trimmings. The fat cap from a Boston butt will also work. Some sold as fat back is salted and may also have cure added, so read the label and make any needed adjustments (ie, wash salt off, or don't include the weight of the fat in your cure addition if you are adding cure to your sausage).
