Since no-one has replied to this thread - I might as well have a conversation with myself
I researched OEM-style slip-on mufflers compatible with the CM400/CM450 motorcycles.
MAC slip-on Megaphone Mufflers 001-0313
Listed as made for the CM400/CM450s. Comes with a "bracket to stop the center stand". Not sure if that could be adapted as a side-stand stop - like what exists on the OEM left pipe.
EMGO slip-on Megaphone Wide Mouth for Honda 24" - 80-84075 (removable baffles)
EMGO Roadhawk Megaphone Muffler Wide-Mouth 24" - 80-84013
5 or 6" longer than the OEM silencers. No side stand or centre stand stop of any kind. The product appearance and descriptions of these two are almost identical, except for the reference to Honda and removable baffles for # 80-84075. Incidentally, #80-84075 is also more expensive.
EMGO silencers came with my CM400, and aside from the side stand making a dent in the chrome on the Left pipe - they seem to work OK.
Marving Approved Exhaust Silencers Honda CM 400 Custom H/2056/BC
Made specifically for the CM400. Comes with an OEM style side-stand bumper on the left pipe.
Probably the most expensive of the bunch, especially because they're made in Italy.
And if I had won the lottery... there's a set of similar brand new original Honda silencers for sale on ebay... in Bahrain.
The Canadian dollar value sucks right now...