As far as i know there are no sports exhaust for the Bis the only way to go is to have one made, if you go on line and check out customized exhausts in your area,
The usual reason for the weld on the exhaust brackets breaking is that they are strained, when i fitted mine i bolted up the two down pipes on the head first, then if you look at the holes on the exhaust brackets they won't align with the holes with the captive nuts on the brackets that are attached to the engine, the idea is to re-drill the holes on the exhaust bracket so when there tightened up they fit without too much strain