I bought everything for my system from here:
https://avinusa.com/10-25-bmw-x1-ser...on-system.html
Mine took a bit longer to install, because I had to install a backup camera and idrive controller as my X1 didn't come with those options. I definitely suggest getting the hardwired backup camera rather than the wireless if you are looking at this system.
Let me know if you have any questions.