There are a few not so common vehicles in Hook 5 Objects download section here and here; but if those are not enough you can extra officially grab my yet still work in progress H5 Object Vehicle Service Pack 1 from >this link< that counts with vehicles from Driver San Francisco including sedans (Cadillac DTS, Ford Crown Victoria LX, Dodge Monaco, Chevrolet Impala LS) pick up trucks (Chevy C10, GMC Sierra, RAM 3500) or classic cars (Dodge Challenger and Cadillac El Dorado) and service vehicles too
There are a few others from other sources; many can be seen on this movie from member @de_lange_jaap
These are part of a delayed project that still need a fix, made for my own use not intended for fancy release yet so feel free to distribute them
About the Viper, I have no clues on its textures