Headers wanted for a 1998 Thundercat

Hi all,

Does anyone have a set of headers to suit a 1998/R-reg Thundercat?

I'm having a hellish time trying to get the bike to pass its MOT because its (otherwise fine) aftermarket headers have a much smaller outlet diameter than stock or aftermarket link pipes. Cutting slots in the link pipe to allow better clamping doesn't work, a shim/ring spacer is out of the question, and apparently there aren't any engineering shops around anymore.

Need it ASAP as the bike's currently in the shop getting other stuff done pending an MOT re-test.