Sirius adapter for 2009 135??

I recently bought a 2009 135 convertible and it came pre-wired for satellite, but it doesn't have Sirius installed.

I asked my dealer about it and they said it required an adapter that plugs into the back of the radio. Then they told me BMW no longer supports this and the adapter is no longer available.

Does anyone know where I can get an adapter? Is there a way to add an aftermarket receiver that will operate with the radio so it plays through the radio/steering wheel controls?

For a 2009 BMW which is prewired for Sirius you need to buy an external Sirius tuner, install it and have the car coded. The brand new Sirius tuner is probably around $700. Used ones on ebay should be half the price.