Clean up crews can be purchased online or from the LFS. What you want is to be selective. I avoid the packaged deals. If you want snails be sure you get ones that are hardy and do what you want. Some types just dont last. Some types only work the sand while others just the rocks. If you want crabs then dont get snails. Snails are crab food and shelter. Even more so in a smaller tank. I try to shop around and get what I need and only what I need. I find Live Aquaria has a good selection. Reef Cleaners has some good things but limited on the snail selection. Reeftopia also has a good selection.