What weird questions and affirmations you do...
Except the official DLCs that all the Forza Motorsport (at least from the third one) and Horizon game series have got, which have all been carpacks, there's no chance to make community made mods for these games, first because they're for Xbox consoles, and second because they're somehow protected from modding (in the specific the three available also for PC so far) and there aren't tools created to mod them.
As far as I know and have seen, there's no chance to get the models of the first Forza Motorsport, which was released in 2005 year for the first Xbox. Of no Forza series game have been converted all the vehicles for MM2, simply because they're hundreds and need lot of work to be converted...
Maybe the cars from some of the newer Forzas (like Forza 5 etc) weren't yet adapted into a suitable level of detail to work in MM2.
Instead no, I guess that also all the recent Forza series games must have the "LOD1" 3D models, which are the ones that fit best for MM2 for polygons count and have been always used for conversions of the cars from these games to MM2.