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Adapters for what exactly? If you just want audio you can use a simple AUX cable if your car has an AUX input
 
Check with the usual suspects for aftermarket interfaces and aux inputs:

DICE, Grom, PAC Audio, USA Spec, etc. See also prior threads on such topics. This isn't an exhaustive list by any means.

If your car has an AUX input, then you can just use an AUX cable.
If you're ok with audio going through the headphone amp. Audio via the dock connector will be cleaner.
 
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