Here you can find the Integrated child seat part #:
https://www.realoem.com/bmw/enUS/sho...diagId=03_3019 It's still a rare part, even in the EU.
EDiT: Found one in Germany, seller doesn't want to ship it though. (EU 90,-)
https://www.ebay-kleinanzeigen.de/s-...3139-223-18072 And another one, in Montana Leather but pretty pricey. (EU 300,-)
https://www.ebay-kleinanzeigen.de/s-...90654-223-5651