I tried to add a car to my models in Valley. A person would think you could find that in skins/models (or vehicle)/CarCommon. Much to my surprise that's not where the Valley car resides. I decided to add my car in all folders CarCommon, ValleyCar and vehicles. No Cigar.
Here's my question: 1 Where do I put the new car so I can see it in the "In Game Menu" under models. 2. Are there any cars for Valley other than the one in the game. 3. Do the cars I used in Trackmania work in Valley.

Cars from tm1 do not work in TM2. A little error shows up at the top. Otherwise Skins > Vehicles > CarCommon works fine for me.

Cxom is correct.
You can get additional cars for TM2 (any environment) from http://www.maniapark.com

Cars from the old Carpark do not work with TM2.