Mark,
This is a matter of Finale language, which in some cases is different from music language.
In Finale language a "left barline" means a barline at the beginning of the system.
From left to right the order is:
left barline, clef, key sig, time sig, measure, right barline.
My guess is that you, if you select a "left barline" in the Measure Attributes dialog box, actually do get a left barline. Only it doesn't appear where you are looking for it.
Since you want - from left to right -
clef, key sig, time sig, double barline, measure, right barline,
I suggest that you insert an empty measure with zero width, and set its right barline to be a double barline.
You can hide the "zero-measure"s default "empty measure" rest with the Staff Tool.
In the Measure Attributes dialog box you can set the measure's width to zero, and you can set the measure's right barline to be a double barline.
If your score should display measure numbers, you need two measure number regions: One measure number region before the double barline, and another region after the double barline.
Playback will be incorrect, because of the inserted "zero-measure".
Peter
PS Another example of Finale language being different from music language:
In music language "articulation" means how you articulate a note - staccato, tenuto, accent &c.
But in Finale language "articulation" means anything you create with the Articulation Tool, e. g. a fermata, a fingering, an accidental.
