question

In the attached model I have two different solutions to this.

Code in On Arrival Trigger

I added a portOrder label to the decision point and generated a randomized list of port numbers. The list is randomized using the algorithm mentioned in this question. Whenever an item arrives it pulls off the last number, unless there are no more, then it generates a new list.

/**Send Item*/
treenode portOrder = label(current, "portOrder");

//Generate the random list of ports if the list is empty
if(!content(portOrder)) {	
	int counts = nrop(current);
	int dummy = 0;
	intarray numset = makearray(counts);

	//Create a {1,2,3...10} array.
	for (int i = 1; i <= counts; i++)
		numset[i] = i;

	//Randomize array
	//For each number i swap numset[i] and numset[j] and 
	//j is a random index between 1 and i.  
	for (int i = 1; i <= counts; i++){
		int j = duniform(1, i);
		dummy = numset[i];
		numset[i] = numset[j];
		numset[j] = dummy;
	}
	
	//Add randomized numbers as subnodes of my portOrder label
	for (int i = 1; i <= counts; i++){
		treenode subnode = nodeinsertinto(portOrder);
		nodeadddata(subnode, DATATYPE_NUMBER);
		set(subnode, numset[i]);
	}
}

//Pull off the last subnode
int nextPort = get(last(portOrder));
destroyobject(last(portOrder));

//Send the item to the port number I just pulled off
treenode newDest = outobject(current, nextPort);
conveyorsenditem(item, newDest);

Process Flow

This time I used Process Flow so there's very little code. Similar to the other solution I have an Event Triggered Source that is listening to the On Arrival event of the decision point. The token tries to pull something off the list, but if it can't (because it's empty) it regenerates the list. A Create Tokens activity creates a new token for each output port and assigns it two labels: 1 - it's port number and 2 - a random number. These tokens then push themselves on the Order List. When a token representing an item pulls from the list it uses an SQL query to order the entries on the list by their second label (some random number). This way you pull off a random number.