Here is a link to a basic clapper. I prefer the clapper with handle. June Tailor use to sell one but discontinued it. I heard it was coming back on the market for quilters now that most know what an excellent job it does for seams. The wood absorbs the heat fast and any moisture if using steam. If you see one at a thrift store or yard sale, grab it. The professional tailor clapper is very expensive.
http://www.nancysnotions.com/product/tailors+clapper.do