British DPM helmet covers were made for the Mk6 helmets and were in both desert and forest variants. Available now are the forest variants that will blend well in most green dominant areas. 
These covers just slip over the helmet and are tightened via a drawstring. On the covers, they will have foilage straps to help you improve your camouflage capabilities. 
 
95% of these are missing the sizing tag but appear to be sizes large. 
These are used, so expect some foilage straps missing, fraying, and/or small holes/tears in the covers.