This is who I bought mine from: Arkon
They actually carry a lot of car mounts for all sorts of stuff from phones to tablets.
This is their cup holder mount with a flexable neck: Mega Grip Cupholder Mount with Flexible Neck
This the one I bought, and it doesn't require the use of a cup holder or air vent. The description says it is
for "smart phones" but my RS Pro96 fits fine: Arkon Mega Grip