Originally Posted by Eric Giles

Probably can't just get them at the parts store, so you will need to get them from a dealer-but not your dealership! These are available online from Tischer BMW for $62.70 plus shipping-and this includes both microfilters. The part number is 64316945585 and their website is getBMWparts.com

Note I am not affiliated with them-just have used them before with great service. You can also change them out yourself fairly easily, although I have not done this on an E70 yet-but from the looks of it, it is no different from most later model BMW's. Access is under the hood at the firewall-remove a couple of covers, slide out the old microfilter, slide in the new one, and reinstall the covers. Done.