You could look for a second-hand copy on either Ebay or Amazon. Alternatively, I believe that John Curry did a compendium of earlier versions of DBA, which will include it. There might be specific information about John Curry's book on Phil and Sue Barker's website. (Not selling my copy of DBA v1.1 I am afraid!)
I do know that they had (and probably still have) a free to download PDF of version 1.0 of DBA, which is fairly close to version 1.1. The main differences that I noticed were:
The authors added the following to the first paragraph of the introduction for 1.1:
“Since DBA is now being used extensively for competitions not restricted to historical opponents, this version1.1 incorporates changes to make it more suitable for this, and to harmonise with its DBM big battle derivative.”
This implies that many (or most) of the changes from 1.0 were for play-balance rather than accuracy.Tactical Moves
The following was added: “A legal move cannot be taken back once made.”
In version 1.0, Light Horse slow down to 400 paces when moving by road, whereas in 1.1, they do not.
The ‘threat’ or ‘Barkering’ zone is 200 paces in version 1.0, rather than the base width of 1.1.Distant Shooting
War Wagons do not shoot in 1.0. but do in version 1.1
There a small number of changes to combat factors:
Artillery went from 3 v foot and 2 v mounted in 1.0 to 4 v foot and 4 v mounted in version 1.1
Warband went from 3 v foot and 3 v mounted in 1.0 to 3 v foot and 2 v mounted in version 1.1
In 1.0, when an element wins when fighting 2 or more enemies, only the one to its front recoils, flees or is destroyed. The other(s) stay in contact. In 1.1, enemies in flank or rear contact recoil.
Warband do not get rear support in version 1.0. but do in version 1.1Combat Outcome
Scythed Chariots are not destroyed by equal totals in 1.0, as they are in 1.1.Total less than enemy but more than half
Elephants are not destroyed by Auxilia or Light Horse in 1.0, but are in 1.1.
Auxilia are destroyed by Scythed Chariots in 1.0, but not in 1.1.
Warwagons are destroyed by everything in 1.0, but only by Artillery or Elephants in 1.1.
Total half or less than enemy
Light Horse are not destroyed by War Wagons in 1.0, but are in 1.1.
Psiloi are destroyed by any mounted in 1.0, whereas in 1.1 the only mounted that destroy them are Knights, Cavalry or Light Horse.