This would be the easiest (not the best) way to do this.

You make a text box control array (12 boxes) with indexes
0 to 11.

You then find out the ascii codes for upper case A to Z.

You then make a Do Loop to look something like this:

It puts the ascii character for A in all 12 boxes
Calculate the sum of ascii codes and if it is the right sum
add the combination to a list.
Increment the character in the last box by one.
Calculate the sum and check if it is the right value. if it is add it to the list.
Keep incrementing the chr in the last box until it reaches the max value (letter Z), then increment the value in the second to last box by one and reset the value in the last one to A.
Calculate sum and check it.

etc.