They are as rare as Rocking Horse Poo! Get your old one welded up.

As has been said before the Bultaco alloy is of good quality and can be welded. If you are going to paint them black then the dressing of the weld is not as important. If you are polishing them, then obviously more effort is required which is half the fun of restoring a classic bike and the end result should put a smile on your face since you have done it yourself.

Was not all that impressed with the quality of the reproduction fiberglass airbox and wanted to use the factory one, but it was badly cracked. Decided I had nothing to lose and heated up the end of a chisel and tried welding up the box with surprising results. not pretty, but solid and since its out out site it worked quit well!