There are a number of stock makers, but the one people usually contact for that is McMillan. www.mcmfamily.com . They'll have the exact stock. As far as the scope, your preference, though I suspect they are using US Optics, which essentially custom makes the scopes. There are others. Personally, I can't see the difference between a good Leupold and the others. But, if your eyes are better, then go for it. My kind of Leupold costs about $550. - $600.US at discount. The fancy ones are $1,000.+ US. A good source for scopes is www.swfa.com which has most of the good brands.
You'll also have to upgrade the M1A to justify all the fancy appearance items. Unless you already have the premium barrels and GI bolts, etc., you will need a Super Match for starters. BAsically you need all National MAtch mods, especially gas piston and trigger. The sights are different, too, but since you ask about a scope they may not matter. Indeed, the standard sights may be more useful at close ranges since you will use the scope for distance. And, you need a Kreiger or similar barrel. The standard and match barrels are good, but the premium is needed to make a true package.
Good luck.