Where to buy: 1. DIN to TRS
The DIN to TRS cable can be bought at usual Vintage Radio Restorers. See below:
http://www.conrad.se/
...and sometimes on ebay
2. TRS 3,5mm + Stereo to Mono Plug
Those can be bought at every Electronic Store in your Hometown.
Note: Use a TRS Cable with a small housing so it can fit to Smartphones without taking the protective Cover off.