KMC makes a heavy duty BMX chain. There's also half link chains. I don't think they look beefy, just different. If you're really feeling it, you might be able to salvage some motorcycle bits for an obnoxiously heavy duty set up. Or fab up some adapters and make a double chain set up (never seen it on a bike). If you've got time to kill and a local (non-box) hardware store, cruise on down and see if they have beefy chain that's 1/2" on center by 1/8." Freak Bikers might be able to help out too. They've got some beefed out contraptions, and somebody may have matching chain.