Like any other fish, you have to fish where the herring are. This means either chasing bait balls with a boat, or waiting for them to show up in spawning areas - Westport in March is where I usually get them. When you do get into them, mix up salt, water, and ice in a bucket and kill them in that. Keep them in the ice brine for a few hours (add salt and ice) until they start to get stiff, then lay them out on a cookie sheet, put them in the freezer for a couple of hours until they are hard, pack them in vacuum bags, and vacpac them. They need to be hard frozen before you apply vacuum or they will crush. If you never let them thaw out and get warm except right before you use them they will be the best baits you ever used.