You can find the part numbers at www.realoem.com/bmw under the section:
VEHICLE TRIM => DOOR TRIM PANELS/LATERAL TRIM PANELS

Match it up for front/rear doors as needed. As he mentioned, it's part #4 in those diagrams (the handles themselves). Should then be able to source from your favorite BMW parts source.

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2002 X5 4.4, Stahlgrau Metallic, 55k miles
Sport, Cold Weather, Rear Seat Heating, Rear Climate, Nav, PDC, Electric Rear Seat Back Adjustment, Rear Shades
Current Mods: M steering wheel, Mk4 Nav Retrofit, Intravee/Alpine/SpecDock, Cosmos Schwarz Interior Trim
Coming Soon: Hood Protector
Wish List: Aluminum Running Boards, Rear Backup Camera, 20" Staggered Style 87s (Black), Hitch Retrofit

1996 318ti, California package (plus tons of mods), Aqua Metallic, 237k miles