Well, I suppose I could write that up, but you don't need to specify the number of sub-matrices in your argument. It will work for any number.
StructureConstantsList = ArrayReshape[PadRight[Alphabet[], 5 3^2, Alphabet[]], {5, 3, 3}];
StructureConstantsList[[All, 2]]
(* {{"d", "e", "f"}, {"m", "n", "o"}, {"v", "w", "x"}, {"e", "f", "g"}, {"n", "o", "p"}} *)
StructureConstantsList = ArrayReshape[PadRight[Alphabet[], 1 3^2, Alphabet[]], {1, 3, 3}];
StructureConstantsList[[All, 2]]
(* {{"d", "e", "f"}} *)
If what you want is a function that takes the lists of matrices as an argument, you can do that easily:
#[[All, 2]] &
Or are you saying that you want the index of the row to be an argument?
RowsByIndex[listOfMatrices_, index_] := listOfMatrices[[All, index]]
