If you are dealing with discrete random variables, you really only need to use the accumarray function.
Here is an example for three random variables with two possible states:
numRealizations = 100;
numStates = 2;
x = randi(numStates,numRealizations,1);
y = randi(numStates,numRealizations,1);
z = randi(numStates,numRealizations,1);
rvCount = accumarray([x y z],1);
To include additional random variables, you can just append more values to the matrix input to accumarray ([x y z t], etc.). Counting the values shouldn't be too much of a problem, however, visualization is another problem entirely!
Hope this helps to get you started and good luck!