Spotted at Toy Soldier's website this Crye Precision AirFrame Rails and Cover Set which they are selling for US$230.00. A quick check at Crye Precision's website and we found out that for the same set, you can get them for US$92.50 (US$43.00 for the rails and US$49.50 for the Cover) which is a better deal and you're assured that they're really from Crye Precision.
This is a nice add-on protection to your helmet as it provides more cover for your ears. This FMA Side Cover for Helmet Rail will need the helmet rail system for it to be installed. It will fit real or replica OPS-CORE systems and it's made of runner and light enough not to add more weight to your helmet. It costs US$13.58 at EB Airsoft, and as always, shipping cost included in the price.