I did a search and didn't see anything about group-c so I am officially putting in my wish list for those cars Loved the Porsche and Mercedes.
OK, let's think of this in a slightly logical way of how this can happen. ISI currently have some sort of deal/relationship with Nissan, Renault, BMW and i believe Chevrolet (i remember a 'vette in preview clips). Now, without going to anyone else, you have 3 cars there as Renault never bothered. BMW had a GTP car at one point: As did Chevrolet: And Nissan had multiple variants: So there are three cars right there without having to venture too far, i'm not sure the Porsche and Mercedes are really possible licenses to expect ISI to get but maybe some of the the chassis makers like Argo, Spice, Tiga, Royale, Alba, Fabcar, and Kudzu?