I've send an e-mail to Rio an askedt them where to buy an car mount.
And this is the answer:
Car mounts will be available from the USA/Canada SONICblue eStore in the
next few days. The UK/International store will have them in stock in then
next month or two.

Fabian
S/N 080000540 12GB blue
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Fabian S/N 080000540 12GB blue