A few things;
If the issue is not gauge but ball end size and the strings are long enough you can thread the strings through bass string ball ends. Guitar ball ends will not pass through a bass' ball ends.
If the issue is availability Ernie Ball makes a Bass VI set (their A string is a .072 which is about right) that is nearly identical to the octave E set - you can toss the E string (or send it to me

) and pick up a single plain .015 or .014 to give you your A tuning.
There is always the single string option - most standard guitar strings will have enough length to let you tune up a bari. Only exception that would negate this may be whether you string through the body.
Good luck!