There’s several old threads about doing this retrofit, just do a search. BMW does not sell the retrofit kit anymore so you have source the parts from ebay. From what I’ve read, the cabling is the hardest one to find and you’d probably have to fabricate one from WDS diagrams.
Once I was tempted to do this mod as well and the parts were still readily available back then. But mine’s a definite keeper so the logic of doing a non-reversible mod to get a nav that is getting more obsolete year after year just didn’t add up.