After purchasing a Ruger SR-556E this week I was frustrated to find that only the Ruger Shop sells rails compatible with their rifle. I know that the rifle hasn't been out for very long and that is probably the main reason Ruger has a monopoly on the accessories. I went ahead and ordered a 9" bottom rail and that was it.
Well searching around I found a site that sells rails for the SR-22, and not only do they fit, they are about half the price of what Ruger is asking! The 9" isn't available because it doesn't fit the SR-22, but they sell 7 inch, 5 3/4 inch, and 3 inch rails. Also other accessories for the SR-22 will fit your SR-556E. I bought a Midwest Industries sling swivel mount
for mine too. Well if anyone is interested in another source for rails and accessories here is the link.
I ordered two 5 inch rails for each side of my rifle and they are identical to the rail I bought through Ruger. I just wanted to relay this info to other SR-556E owners. Hope this helps some of you guys...