I was recently at the ICF (vcf.org fscked up the dates - 9/30-10/1) and I spent my time imaging a lot of disks - including over 100 NorthStar Horizon disks. They're up for download at http://annex.retroarchive.org/disks/ICF%20Disk%20Images/ - see the "Northstar Horizon" directory.
Enjoy!
g.