I'd start with a box of Federal Gold Medal Match ammo with 168 grain Sierra Match Kings or a box of Black Hills 168 grain Match. There are a number of other makers of match-grade .308 Win ammo. You might even be able to get some surplus 7.62x51 NATO ball match ammo at a gun show.

But if you're serious about accuracy, there is no better ammo than the kind you make yourself by handloading. Then YOU get to control the precision and quality of the ammo and taylor it specifically to your rifle. Factory match ammo is pretty good stuff, but they still are limited by having to load it to be safe in every rifle chambered for that cartridge, which leaves room for error.

Mike