The Stag 7 is a good choice
Building one from an ARP barrel and bolt is a good choice.
Iron Works Tactical can build you one with APR parts and in fact has some in stock right now.
He builds excellent weapons.
Here is a list of 6.8 manufacturers:
Complete 6.8 SPC rifles
1: Armalite
2: Bushmaster
3: Rock River Arms
4: Stag
5: LWRC
*6: Wilson Combat
7: Daniel Defense / Ambush
8: DoubleStar
9: DPMS
10: Barrett
11: LMT
12: Robinson Arms
13: 2 Vets
14: Yankee Hill Machine
15: Palmetto State Armory
*16: Ironworks Tactical
17: Country Boy Sports
18: PRI
6.8 SPC upper assemblies
1: Stag
*2: Ironworks Tactical
3: Suppression Solutions
*4: Wilson Combat
5: Yankee Hill Machine
6: Palmetto State Armory
7: White Oak Armament
8: State Of The Arms
9: Rock River Arms
10: Red X
11: SOTA
12: Precision Firearms
13: Surplus Arms and Ammo
14: JSE
15: CBA
16: Delta 3 Tactical
17. Armalite
18. Blackstone Arms
19: Bushmaster
20: DPMS
*21: Bison Armory
22: PRI
23: Rainier Arms
24: Blackthorne Products
6.8 SPC barrels/bolts/other parts
*1: AR Performance: Barrels and bolts
*2: BHW: Barrels
*3: Wilson Combat: Barrels,
4: Palmetto State Armory: Barrels and bolts
5: Stag: Bolts
6: Yankee Hill Machine: Barrels and Bolts
7: AR Stoner (MidwayUSA): Barrels, Bolts, and Magazines
8: Daniel Defense / Ambush: Barrels and bolts
9: PRI: Bolts, magazines, 6.8 specific breaks
*10: CProducts Defense: Magazines
11: ASC: Magazines
12: D&H: Magazines
13: MagPul: Magazines for LWRC Six8 platform
14: DPMS: Bolts
15: White Oak Armament: Barrels
16: State Of The Arms
17: Red X Arms : BCG
*18: Mad Dog Weapons Systems: general 6.8 retailer
19: Treasure Seekers: 6.8 bolts, marked carriers, dust covers, etc
*20: Hamlund Tactical: general 6.8 retailer
21: Rainier Arms: Barrels
22: Integrity Arms: Barrels
23: Douglas: Barrels
*24: Bison Armory
25: Stutts Tactical
*26: Ironworks Tactical
27: AIM Surplus
28: Blackthorne Products