There really isn't a 6ARC BCG right now, because 6ARC uses the same BCG as 6.5 Grendel.
There are some manufacturers that label their BCG's 6.5Grendel/6MM ARC, but the bolt face is the same.
You may have better luck looking for a 6.5 Grendel BCG, or even just a Grendel Bolt married to any AR15 Carrier will work.
It's been slim pickings online in general, (I'm building a 6ARC as well right now). I've resorted to piecing together with a new bolt and pulling a carrier from my parts bin.
AIM Surplus had 6.5G Bolts last I checked for a good price, and I believe Ballistic Advantage had some full 6.5 Grendel BCG's in stock if you're looking for budget friendly options.