I have M4-style handguards on my AR Carbine.  I'm trying to find a rail to mount to the top of the handguards for attaching an offset light light mount.  Problem is I can't seem to find a rail that has a built in slope to keep a light parallel with the bore.  All of the rails I've seen are just simple rails with no slope that will basically point the light with the downward slope of top of the handguards.  Anyone know of a tapered rail?
Thanks,
Mainrotor

Denny's guns used to sell one, still may. Or you can just switch to a set of M4 non-tapered handguards.

Yankee Hill makes that tapered rail (slightly taller in front to accomodate the slope of the handguards) that you are looking for.  Bushmaster has them in their catalog and possibly also Brownell's.

Midewest Industries makes a nice one.

I like the Daniel Defense one:



But then again, I have a Troy MRF-C on my AR.

I mounted my light with a section of Weaver rail bolted through the HG’s. By drilling the rear hole first I was able to pivot the rail into the correct position for the lights throw. A pack of Weaver 1” rings and a section of rail was about $25. Shimming, as called out in the link, was not required in my case, the light throw was perfect as is.

Follow this link for DIY instructions.

How to Make a Flashlight Mount

I just put the rail in the Offset position and eliminated the offset mount.