A had a similar problem a couple of years ago, where I wanted a 7-segment display in a PC program.
I found a freeware component that did the job, but it was very crappy looking.
So I decide to write my own, but like you, could not find any mechanical/dimensional specifications for 7-segment displays.
To get the mechanical specs, I searched the web for the highest quality and resolution image of such a display that I could find, and wrote a program whereby I could "digitize" the coordinates of each corner of each segment by clicking the mouse over the hi-res image.
My final result was a very realistic simulation of a PDP11/34 console:-

which can be seen operating in this video:-
The definitions for the segments that I used in my code are:-
// Map of segment vertex coordinates
Const SampleSizeX=1714; SampleSizeY=2638;
SampleSegVertices: Array[TSegmentID] Of Array[1..6] Of Array[1..2] Of Integer=(
(( 311, 66),( 375, 1),(1577, 0),(1633, 63),(1376, 302),( 520, 301)),
((1650, 96),(1714, 160),(1593,1325),(1451,1321),(1312,1171),(1400, 324)),
((1442,1357),(1587,1364),(1474,2495),(1400,2557),(1193,2335),(1277,1504)),
((1379,2575),(1311,2638),( 140,2634),( 85,2574),( 329,2350),(1171,2351)),
(( 64,2545),( 0,2484),( 110,1346),( 253,1353),( 391,1501),( 312,2328)),
(( 250,1317),( 109,1309),( 215, 155),( 287, 94),( 499, 326),( 420,1162)),
(( 277,1333),( 434,1188),(1282,1188),(1418,1335),(1258,1484),( 411,1480))
);
Each row is for one segment, each of which has six corners at the points specified.
SampleSizeX/Y are the width and height of the whole digit.
From those numbers, I think it would be fairly easy to scale those coordinates to whatever size you want.
Hope that helps...