Go to lowes.com and search "mirror hanger." One possibility is their item # 61002 which "The Hillman Group Mirror and Picture Hanger" model #122201. I was there today and they had lots of 'em in 4 piece packs.
You probably want the plastic ones rather than the metal ones. In thinking about it, the "cup" section of most of the slotted metal ones may not be wide enough to hold matte + glazing without pinching.
Looks really nice on the wall, as is obvious in the video. The trick is not to tighten them so much that the glazing is stressed which creates reflective ripples. The whole thing should be just loose enough that you can slide it left and right without too much effort.
When my friend did a show with these he found that dust could accumulate along the top and work its way down between the glazing and matte. The cure was to put thin strips of pressure sensitive clear tape along the top and trim flush with an Xacto knife. Remove immediately after the show to avoid adhesive migration.