Been looking for the same, got a few bits in the spare parts bin. (Currently riding an Arkose – which is great – but the wife wants to have it for her commute.)
Needs rack and guard mounts.
So far:
Kinesis 4S disc frame-set – very expensive for an ally frameset but quality. Flat mount disc compatible which is nice.
Cotic Escapade – heavy with a very tall head tube and no carbon fork.
Genesis Croix’s or Equilibrium disc – heavy and expensive.
Otherwise it’s a complete bike such as Arkose, Norco , Marin, GT Grade et all, can’t seem to get frame only options.
Jameso reckons Pinnacle Dolomite disc framesets will become available in a couple of months so possibly Arkose framesets will come online too?