There are 4686825 possible combinations, so I would recommend not storing all of them, especially not in numbered variables, which are a bad idea.
idx=nchoosek(repmat(1:3,1,9),9);
a=cell(1,3);
a{1}=[1,0,0];
a{2}=[0,1,0];
a{3}=[0,0,1];
n=1;
current_combination=cell2mat(a(idx(n,:))');
But if you insist, you can use the code below. Note that it takes a lot of memory and a lot of time (about a 4GB increase in RAM usage and 3-4 minutes on my machine (W10x64,R2019a)).
idx=nchoosek(repmat(1:3,1,9),9);
a=cell(1,3);
a{1}=[1,0,0];
a{2}=[0,1,0];
a{3}=[0,0,1];
total=cellfun(@(n) {cell2mat(a(idx(n,:))')},num2cell(1:size(idx,1)));
total=reshape(total,1,1,[]);
total=cell2mat(total);
