http://www.wemoto.com/bikes/Honda/CX_500_CB_Custom/81-84/Have down pipes and silencers
I had a CX "back in the day" and after 3 years the original silencers were shot so the chances of getting S/H is remote, you used to be able to get a after market collector box, basicly it was 2 pipes with another connecting them together, someone useful with a welder should be able to knock one up
Try an avoid 2-1's mine ran cr*p, it was a lot nicer bike with the original setup