A nice source of small-celled sponge is from the cosmetics section of any department store. The local Daiso sells a variety of sizes. Another possibility is polyurethane sponge from the kitchen cleaning department (this is often sold as "magic sponge"). Since it's mildly abrasive I don't suggest using it to clean rubber sheets though it does work for water-based rubber glue. I don't use any of these since I use Elmer's Rubber Cement (there's a nice brush under the cap). There's absolutely no way my bats will ever have to go through VOC testing. Clips? Maybe small bulldog clips, or just cut your sponge bigger..