I believe those bulbs were used in Camaros (PH16W?), but little else. Not sure there is a Txx base replacement.
EDIT: Found this listing on Amazon:
http://www.amazon.com/iJDMTOY-2011-13-BMW-2014-up-Reverse/dp/B00F4K02JA
iJDMTOY 25W CREE PW16W PH16W LED Bulbs For 2011-13 LCI BMW E92 328i 335i M3or 2014-up BMW F32 428i 435i M4 Backup Reverse Lights
by iJDMTOY
Price: $99.99
Sale: $59.99 & FREE SHIPPING
You Save: $40.00 (40%)
Note: Not eligible for Amazon Prime.
In Stock.
Ships from and sold by iJDMTOY Car LED Guru.
•Compatible with 2011-2013 BMW E92/E93 3 Series coupe with LCI LED tail lamp or 2014-up BMW F32 4 Series
•2 pieces 25W Max PH16W LED Bulbs
•1 piece CREE R4 LED on top with 3x Optical Lens for sport light + 4 pieces CREE R4 LEDs on each side for flood light
•5x brighter than stock bulb and 2x brighter than competitor's LED reverse bulbs
•Lighting output: approx 500 lum