you might check with Wynn Environmental - they make MERV rated filters for industrial, woodworking (most common dc) and ambient air cleaners. All made in USA; they're good people to deal with, too. The nano filter cannister for the HF 2hp dc is MERV 15. I've been using it for 3 or 4 years now with excellent results..
Not connected with them, just a happy customer that's converted three dc systems to them over the years.