The DR200 years 1986 t0 1988 used a strange 28 mm flat-slide carb with a similar plug-in fitting and even the same sort of throttle cable assembly. It was called a TM28 and was also used on the XR200 and others. Looks like this:



The trouble is that they're getting rare and cost something in the region of $280.

If you google "mikuni tm28" there's quite a lot of info on them, some people swapping them for the VM26, quite a famous performance carb I read a lot about. It looks like this and it's also a plug-in fitting, rather than a flange fitting, which I wrongly assumed was normal on slide carbs.... The only thing is that you'll need a throttle cable. They're also a lot cheaper (around $140):