I have used the companies mentioned above by Mr H and all are good recommendations. Fine when you have enough time to plan purchasing. I have also used Frank Keane’s as mentioned by Dergside for handiness and if I needed items more quickly and Nick in parts has been extremely helpful as have his colleagues before him. But any BMW dealer with be OE and not OEM. For OEM Car parts pros would be an option. On a more local level I have used OTTO and have been happy with prices and service.