I've had two; one a MK1 and the other a MK2. The MK2 must have been one of the last brought into the US as it had a Chrysler Penstar on the lower fender as did the last of the Alpines imported. Acquired it after getting a call from a friend telling me if I wanted three Imps in NM (I lived in Denver at the time), that if I could get there by the weekend, I could have whatever I wanted for $100. Hooked up the trailer, made the 10 hr drive, and brought back only the MK2 and a load of parts. Unfortunately, the other MK1s went to the crusher the next week.
Both cars started out as unrestored but with low mileage as Imps traditionally blow their head gaskets at 30K miles. The MK1 however was complete and had been preserved by Paul Dierschow / Sportscar Craftsmen in Denver. I prepared it to more or less stock with a Sport intake (twin carbs). The MK2 I acquired several years later was full blown built, taking advantage of the better suspension geometry and having a Hartwell built 998cc engine. I prepared it in anticipation of running with Rocky Mt Vintage Racing but then converted it to street use before selling it in 2002. In fact, the MK2 was featured in GRM back in Feb. 2003.
Both cars were from the southwest so rust was not an issue except for around the battery tray and beneath the rear window where the rubber gasket had leaked. Rubber pieces were unavailable for doors and windows back in the '90s; maybe that has changed. Mechanical bits were readily available for suspension and engine. Impwerkes in NZ was my biggest source of parts as they were easy to work with and shipping use to be more reasonable from NZ than from England (don't believe that is so any more). Malcolm Anderson in England was also another good source for stuff but don't know whether he is still in buisness. Unfortunately, Hartwell has long since closed their competition department where all the best modified stuff came from.
Were I looking for another Imp (other than to keep an eye on eBay for one of my old cars), I would join the Imp Club and contact the US representative. Years ago, that was Brent Kassel out in Nebraska (I think). Contacting individual owners might result in someone selling their car. Word of mouth is your best bet for finding one.
Ironically, I just found out the fate of my MK1. Back when I sold it (12 years ago?), it went to an ex-Rootes Group employee who had moved to the US after Chrsyler bought them out. Being English, he had always wanted one. I recently sold a BMW R80RT to a gentleman from upstate NY who also worked for Chrsyler. Turns out, Bernard, who had purchased my MK1 Imp had been his boss when he worked in Detroit and reportedly the car is now back in the southwest where Bernard retired to.
Good luck with your search. Of all the cars we have had over the years, it was the Imps that put the biggest smiles on our faces. Always lived in fear of something breaking on them as they seemed so fragile but they were a hoot to drive. If you find one, hang on to it. My MK2 is on my short list of cars I wish I had kept.
Tony