Lumped in with them are vehicles which are, for the most part, either on hiatus (Ridgeline) or in the midst of cramped production (Grand Caravan, Town & Country), or awaiting soon-coming replacement (Maxima, TT).
In terms of the lowest-volume vehicles in America, aside from the discontinued vehicles, the majority are vehicles intended to be low-volume products: 918 Spyder, 4C, Viper, R8.
You can always select a make and model at GCBC’s Sales Stats page to find historical monthly and yearly sales figures from both Canada and the United States. Pertinent links are clickable at the bottom of this post, but you can also find related links at the Best Sellers page.
Source: Automakers & ANDC Vehicles which sold at least once in May 2014 but not at all in May 2015: Mercedes-Benz CL-Class, Chevrolet Avalanche, Acura ZDX, Subaru Tribeca, Lexus LFA, Volkswagen Routan, Volvo C30, Volvo C70.
Aston Martin, Ferrari, Lamborghini, Lotus, Rolls-Royce do not release monthly sales data. Bentley and Maserati do not report model-specific sales data.