I would call Eric at Possum Hollow.
I just ordered Bore Guides for 204 Ruger, 5.56, 6.5 Grendel, 300 HAM'R, and 22 LR. I am sure that he can make one for the 6 ARC. I have made two orders lately. I have gotten both orders in under a week.
If you have multiple AR Bore Guides it would be handy to find some one who can engrave them for identification.
EDIT: My Possum Hollow Bore Guide for my 6.5 Grendel works just fine for my 22 ARC. I am sure it will work just fine for 6 ARC also.
Bob R