In the first editions of Gerald Wingroves superb and unique book; 'The complete Car Modeller' there is detailed a very clever little tool made from a piece of industrial hacksaw blade and shaped like a backward facing tooth! I can attest that it works extremely well when run across thin sheet against a straight edge.
For cutting thin sheet accurately I sometimes also use a small cutting disc on a Dremel…..clamp the workpiece to a piece of plywood and make sure to use eye protection. This method is excellent when making small detail cuts in thin workpieces.
lastly, I cut thin discs for clock wheels by using a specially made trammel adjusted to the exact diameter,…this basically cuts thru the brass when revolved by means of a 'knife tool'. I sometimes use the same basic method on a square piece mounted on an arbour in the lathe to cut out wheels.
Finally (?!)…there is an Eclipse sheet saw which works very well,..it looks like a small panel saw but has a hacksaw blade built into the edge, thus allowing any depth of sheet to be cut.
Interestingly, I don't any longer use a scroll saw to cut thin brass as I did not like that method, although many people do use it quite successfully.