I faced this exact problem with my arkose, here’s you essential options:
‘normal’ 1.1/8th inch steerer 700c road disc fork (for the correct a2c measurement) such as a on one pompetamine steel fork, kinesis DC37, these or similar from German sites: http://bike-x-perts.com/bike-parts/forks/drossiger-cross-disc-gabel-matt.html All have 1.1/8th inch non-tapered steerers which you will then need to get a Hope HS136 crown race reducer to get it to fit with a internal 1.5inch lower bearing. I have done this and it will work perfectly, but the headtube may be fatter than the fork crown, so may not look as pretty!
OR: much rarer to source, a tapered 700c disk fork – just make sure the taper is 1.5inches, as some road forks had a 1.25inch taper (thanks to ‘standards’) and you can’t get a reducer for that anywhere. You can get full carbon jobs for about £120 from aliexpress with the correct a2c measurement, or kinesis do the CXD for £200+, otherwise it’s a bit of an internet trawl. This will work with a normal internal headset.
There are other forks out there but aren’t cheap. There’s a bit of a hole in the market for tapered road disc forks, but this should improve as CX has seen sense and there are more disc ‘road’ style bikes out there (see the latest genesis range)..