Pete
You can get 6v or 12v replicas for about £70 which is what I went for in the end. Taff the Horn can supply genuine refurbed Altettes or refurb yours but you will need deep pockets.
Jim
I looked at Taff's site and deep pockets is true enough. Funny but spending £150 on a speedo refurb didn't worry me where £70 - £120 on a horn seems ridiculous especially when the reason is about little else but aesthetics. My bike isn't standard in many respects so why should a japanese hooter worry me ?
I'll check out the possibility of a graft into the Altette body though.