The original rail ladder covers for the Daniel Defense RIS-II on the M4 Block2 and the Mk18 are from Ergo. Here are the original FDE Ergo rail ladder covers. Pretty simple, but this is what you need to finish your clone, or maybe to start a new project...
Set of three (3) Ergo rail ladder covers. FITS ANY PICITINNY RAIL
(gun not included)
Daniel Defense
Daniel Defense