What you are talking about is the Springfield Armory, Inc. M1A.
They stopped putting bayonet lugs on the flash-hider after the Clinton Assault Weapons Ban and never started putting them back on after the ban sun-setted within the last few years. I got a new flash-hider, with the bayonet lug from Fulton Armory for about 50 or 60 bucks I think. They even have the bayonets there too, if you want one. Make sure you get the flash-hider castle-nut pliers as well, otherwise it is a pain in the pecker to get that pesky flash hider on and off, you might end up ruining your castle nut and the finish as well without it. That little set of pliers makes the whole process easier!
Here is Fulton's website: http://www.fulton-armory.com/
Just scroll down and click on M-14 parts and accessories, scroll through there 'til you find what you need.
My current favorite weapon in the home arsenal!