Bit of a hen's teeth item there mate, being the RHS one.
If you have a down-pipe you could always seek out a CD125 / CD125A early (6v) exhaust in the far East/Japan. It's the ---230--- part and essentially the same silencer but different bracketry. They do pop up on Yahoo.jp ..Plus the CD125 was sold in fairly large number in France. Not cheap to ship though. If you did get one I think the down-pipe is the same as the SS125 so could be sold on for a fair price.
I will keep my eye out on Yahoo Japan.
Bit of a long shot but you could try Dave Mathieson in York ... He has lots of old Honda stuff .. bought the remains of Queen Park Motors parts stock when they eventually closed and other dealers old stock I believe.
https://www.ebay.co.uk/sch/i.html?item=134519389979&rt=nc&_trksid=p4429486.m3561.l2562&_ssn=davgeomatOther than that try and prize out a sale of a NOS pair by the guy you got the bike off ... although I suspect he would be asking big bucks if he did sell. The last NOS pair I sold about four years ago a guy snapped my hand off at £720.