You need a D1S 4300k bulb. Usually sold as Osram, Philips or Sylvania. They are all virtually the same. I think the oem ones are made by Osram, but not a big deal.
4300 is the color of the light, pure white and matching the other bulb. Going higher makes the light bluish as you see on some cars.
You should be able to get the bulb for around $40. Just google or look on ebay. Get a new one that is DOT stamped. Otherwise they are Chinese replicas.
Styling: M5 body kit, M5 trunk spoiler, LED Angel Eyes, HID fogs, LED side markers, Jehnert Flatline speakers, Mobridge M1000 DA2 prepro, Zapco Z8 DSP, Zapco Z-150.6 amp, iDock on dash
Performance: JB4/G5 ISO flashed on Cobb, Meth Injection, AR Downpipes, ER FMIC and Charge Pipe, DCI, Walbro LPFP, RB turbos. H&R Sport springs/Koni FSD shocks.