Where is the map that has all the previews of the props?
They're in the same place as the directory i mentioned earlier in this thread. They're called ABS_PropLibrary_Part_A.vmf, Part_B, and Part_C respectively.
Part A has general decorating props like vehicles, track pieces, and crates;
B has skybox props and out-of-bounds props like cliffs, trees, and buildings;
C has railings, fences, doors, windows, and stairs.
They're split up into 3 vmf's because hammer can't handle loading all the props at once. Also, the vmf's don't have all of the props in existence, just the more commonly used ones.