Although the local shop said that you can't can a Guzzi, it appears that you can – in quite a variety of ways. Most have been mentioned on the site here, particularly in the FAQ. So I have sent the shop this list (doesn't include every option) to see if they will investigate and decide if they might be able to supply any.
Has anybody seen/heard/tried the Venom road legal silencers?
Moto Guzzi's own Ti kit + ECU
Bos: round Alu M00125A, CF M00125C
Carbon Can Co
Fast by Ferracci: F33700 CF slip ons, F33700T Ti
Galassetti: high level
Gianelli : Maxi oval racing Alu 73317A, CF 73317C1, Ti 73317T1
Leo Vince: Leo vince SBK Alloy Type: KR Alloy 5431, Carbon 5432, Ti 5433
Mistral - lots of options: Round aluminum, Round carbon, Oval carbon
Raceco: SS oval; balance pipe
Renegade: Round & oval SS,Ti, CF
Shark: Alu & CF
Staintune: Oval, Removable Restrictor
Venom: road legal oval cans titanium