You can get them for $48/per side at Tischer:
https://www.getbmwparts.com/parts/20...agramCallOut=4
I'm not seeing an actual part number. There is a DIY install on the carbon fiber mirror caps (which are secured differently than the standard covers) which explains how you remove the stock caps. I'm assuming the sport line caps will snap into those same tabs the body color ones were attached with.