Chris: first you need to create a column vector with the desired number of 1s and 2s in the column. Then you need to use randperm() to scramble the order and stick it in your output array:
num1s = 10; % Whatever you want
num2s = 10; % Whatever you want
% Make a column vector with the specified number of 1s and 2s in it.
unscrambled = [ones(num1s, 1); 2 * ones(num2s, 1)]
rows = length(unscrambled);
columns = 16; % Whatever you want
output = zeros(rows, columns);
% Scramble and place into the output matrix.
for col = 1 : columns
sortOrder = randperm(rows);
output(:, col) = unscrambled(sortOrder);
end
output % See it in the command window.
