Looking to get a slightly-larger-than-bike can with an integral cat... anyone have any suggestions?

If you've got deep pockets, Westfield do just what you've just described for their Megabusa. Yes, I have one, and yes it does the job for the MoT, it's also passable on the less NIMBY-affected circuits.

When this burns out, I'll be going for a bike can with an in-line catalyst (e.g Jetex).

Tube engineering Peterborough, do them.

do you have contact details for them?