You may want to ask this question on the restorationmini.com site there are a couple of guys from Maine that post occasionally, they may have an answer in regards to their driving "season".
'92 was the right around when they started putting some pollution controls on carbed minis just before they switched to SPI and cats, my early '92 1275 carb had some rudimentary pollution equipment most of it was removed before it got here, I don't know if the 998 had anything.

You won't want to drive the mini once they salt the roads which starts in September in Maine doesn't it

IMHO, it would not be possible to retrofit emissions control equipment to a pre-emissions Mini, if your pollution standards are anything close to Federal 1992 requirements.

To meet those requirements, you need a three-way catalytic converter, which in turn requires an oxygen sensor and a electronically controlled fuel delivery system - either a electronically controlled carburetor or fuel injection. Neither of which come with a 92 Mini. It's not just slapping on a cat converter.

The most feasible way (though not cheap or easy) I see to do this is to transplant the driveline, ECU, and cat converter from a later injected Mini (easiest would be a SPi model.) Or do a Honda B16 VTEC swap keeping all the emissions gear.

Probably easier to buy a fuel injected Mini. You'd get a 1275 engine out of it too, since only the 1275's received fuel injection. Those will have catalytic converters. 

BMW owned Rover, who made the mini, in Rover's last few years. I don't remember the exact year but they eventually perfected fuel injection for the Mini and emission controls to meet European emission standards. I would say at this point the mini could have been imported to north America except that it did not have collision resistant bumpers. In the mid to late 70s Minis destined for Canada had jury-rigged bumpers that met the NA standards of the time but no other country received these Minis. To meet bumper standards and other standards required a complete re-design hence the advent of the new, fatty MINI.

I am considering purchasing a 1992 MINI City with the 998cc engine. The car is currently in oversees shipment and when received, emission control equipment installed can be inspected, but my understanding is that it is unlikely that the car is equipped with any such equipment. I live in ME and while you are permitted to drive a 25 year old car without emission control devices, you are limited to use during the summer months only.  

To extend my driving months, would it be possible and cost effective to install a catalytic converter and/or other emission control equipment?

Thank you!

jg54