There are lots of stocks available for the American, but most of them replace the entire stock, including the magazine well (a separate piece), so they lose the ability to use AR mags. There is apparently an MDT chassis that retains that ability.
I recently sold a Magpul Hunter stock that I used for awhile on mine. It used AICS mags, not AR ones, but the main reason I sold it was simply because it felt like I was putting lipstick on a pig. It turned the light, handy American into a heavier, much less handy rifle that no longer filled the niche for which I had purchased it. I have other rifles...heavier, perhaps more accurate, certainly less "carryable" than the Ruger. Dressing up the Ruger didn't make it better than those guns, but it certainly made it worse as a cheap knockaround gun than it was in stock form.