I had a set of Unit Blocks, often found in preschool and kindergarten classrooms, that I had picked up at an auction and gave to my grandchildren. They are made of hardwood and last FOREVER! I grabbed three of the 5x2.5x1.5 blocks and use them as clappers. They absorb the heat and are heavy enough to do the trick and in this case free. And the sound of the blocks being stacked away for the day brings back sweet memories of my days as a preschool teacher and director. Great tools can always be used in more than one way. Blocks = clappers!
The hubby of one of my quilting friends made some but in my opinion they are not heavy enough, only about 1/2 inch thick and don't do the job as expected.