I also used Testors Dullcoat for a while, but when I moved my painting inside the house the odor of it was too much for the better half and kids.
So while walking through Michael's of all places. I saw a product by Delta Dreamcoat Matte and Dullcoat finishes ( there is also a gloss finish too, but i am not giving up my Future).
This stuff comes in a 4 or 8 oz bottle. Can be applied with an airbrush or regular brush right out of the bottle with no thinning or mixing needed and dries just as flat as Testors if not flatter than Testors dullcoat.
The biggest factor for me anyways was. This stuff is waterbased, non toxic, dries in 10 minutes and has absolutely no odor at all. In fact on the back of the bottle it states it is for indoor use.
Paul