If you are not fussy about originality there are good quality replicas of the Norton peashooters and Dunstall Decibels, etc, around - Flatracer in England or Trojan Classics in Oz usually have them.
Some of the classic guys stateside have them too, at a considerably higher price.
I have a Decibel with a Overland 2 in 1 system on my R75/7 and it fitted straight on to the OEM bracket.
It has a long straight taper like a Hoske, has better than OEM chrome, sounds better than OEM and flows a bit better too - the stock muffler struggled to cope with the flow from a 2 in 1 but the decibel copes fine.
Adelaide Hills, Australia. 93 R100 GS, 77 R75/7 ,70 BSA B44VS, , 86 R80 G/S PD, 95 BMW Funduro F650 ST