Okay, so I have been studying the music of Joe Pass and he loves to substitute minor seventh chords for dominant seventh chords. For example take a typical vi-ii-V-I progression on C, instead of playing a minor he would substitute for it perhaps a A 13 flat ninth chord. If I am soloing over this type of progression I know I can use the whole-half-step diminished B flat scale over the A altered chord (A13 flatted ninth with the following voicing: A-G-C#-F#-A#). What other scales can I use over this and other sorts of altered chords?
1 b2 b3 b4 b5 b6 b7
So, in C:
B C D Eb F G A
Relative to A:
A Bb C Db Eb F G
This gives you, functionally: 1, b9, #9, 3, b5, #5 and b7. (If you played this against a C7)
In your case, over A13b9: A Bb C# D E F# G.
A great ressource for 'which scale over that chord' in a jazz context is http://www.jazzbooks.com/mm5/download/FREE-scale-syllabus.pdf from Aebersold.
In your case, the only scale listed is the Half-Whole step diminished scale. This does not mean it is your only choice, only that it is the reasonable scale implied by the composer when writing A13b9.