Swanny has a page about using Future...you can add different amounts of Tamiya flat to obtain varying "flatness" of final coats.
http://www.swannysmodels.com/TheCompleteFuture.html
What about the big square bottles of Testor's dullcoat, I believe it to be lacquer. Is that what you all are talking about when you mention Model Master flat coat? I have two big bottles of the regular Testor's at my bench, it works great, but you have to use lacquer thinner. It's very flat.
On Bench: AM P-51B, Tamiya 1/48 F4U-1A
On Deck: Hasegawa F-14's (too many); Tamiya P-47D; Academy P-47N;