Yes - It is typically called an Optic rail.
Critical DImensions has a few left to sell here on this thread:
http://fnforum.net/viewtopic.php?t=3821 for $87.50. His is an slightly extended rail that extends off the back.
MPF also sells one, and I think he has a sale (U just missed Critical Dimension's sale):
http://mpftech.4gunlovers.com/182.html
These are two of our sponsors - but there are also other brands of optic rails out there as well. Magazine Parts.com, another sponsor here, sells one at :
http://www.magazineparts.com/productDisplay.php?id=TOR It is $95 (this is the one I have - back in December, there were a lot fewer choices. This is a great rail, though).
There is also a factory one, but it is about 2x the price of some of these.
U just use an allen wrench to remove the stock sight and attach a rail. Take less than 5 min, and requires no skill at all (so I was able to do it :x )
