Charismatic Megafauna said:
You said you already have ARs, why is this not the answer? https://palmettostatearmory.com/psa-18-rifle-length-6-5-grendel-1-8-stainless-steel-15-lightweight-m-lok-upper-with-bcg-ch3.html
Or this https://www.brownells.com/gun-parts/rifle-parts/rifle-receivers-parts/m1500-mini-6.5-grendel-barreled-action/ and this https://www.boydsgunstocks.com/accessories/plat-howa-1500-mini-dbm-hvy-6-bc-2dc198743zz can't seem to link directly to the stock... it's item 2DC1988041ZZ
You can easily build an upper in 6.5G, I might even have an extra upper I am willing to part with to help out. Or go to a local gun store for help.
Burdett & Sons, Circle Star, etc.