The Opel Kadett B was sold as a 2 or 4 door sedan, a station wagon, and a coupe. The 4 door came in both notchback and fastback body styles. These cars may have been small family cars, but their lack of amenities did not match with the tastes of American buyers. These cars were sold at Buick dealerships, usually under the name Bellet Gemini, but they seemed to have nothing in common with anything Buick has ever offered. They were a car designed to compete with the VW Beetle, but the Beetle was a car made for the less-than-wealthy utilitarian hippies, not for the average family.
GM, which owns Opel, got into a little tiff with Car & Driver magazine over the Kadett B. The magazine reviewed the car, and they may have been a bit harsh. Actually, it may have been the most scathing review of a car they have ever given. Let's just say that the photo that when with the review depicted a brand new Opel Kadett B sitting in a junkyard with some rotting piles of automotive history. Ouch.
The special performance version of the Kadett B was called the Kadett Rallye, while a "luxury" version was called the Opel Olympia A.
These cars can still be found in the United States. There are some Opel dealers who sell the classics, but chances are there are none in your area. There are also a few companies that deal exclusively with old Opel parts, and they probably deal with some used Opels. The best place to buy a classic Kadett B is on eBay, where you can also find some parts.