I got my head unit from carsequipment on eBay. He's in the Czech Republic (where the HU is manufactured.) It was around $370 shipped, and got it within a week.
http://www.ebay.com/itm/BMW-professi...0c4225&vxp=mtr
The install is very easy. The hardest part was routing the mic. Once I figured out how to remove the passenger side pillar, it was all downhill from there.
Here's a YouTube video that got me going down this path in the first place: