There are some stock handguards out there with rails on them but not many. You may end up having to buy a whole other gun to get what you're after weather it be working or broken.
There also is the option of making your own. I now own about 6 various magpul vert grips and AFG's and every one has come with at least one little rail to attatch to a standard military type or an MOE handguard. These would be perfect for what you're wanting to do. You'd just need to drill the holes, then bolt them on. It would be very simple.