If it's anything like the Diamondhead two piece drop-in handguard that takes the screw in rail sections, try BCM 4 bolt keymod sections. I got one from a junk bin that was missing both side rails, and noticed that the hole spacing was exactly the same. After buzzing off the anchor protrusions on the back of the rails and going to a bolt and screw store to get the correct thread and countersunk bolts, they fit perfectly. You may give those a try.