how to extract double itemset from sortedList

Question

(1): 4
(2): 4
(1 2): 3
(3): 4
(1 3): 3
(2 3): 3
(1 2 3): 2
Above are show my sortedList.
may i know how to extract the double itemset and store in another new sortedList?
my expected output in my new sortedList are:
(1 2): 3
(1 3): 3
(2 3): 3
(1 2 3): 2
  below are shown the coding for my sortedList1:
 foreach (String sort in lbCombinations.Items)
            {


                if (!(sortList.ContainsKey(sort)))
                {
                    sortList.Add(sort, 1);
                }
                else
                {
                    int Count = (int)sortList[sort];
                    sortList[sort] = Count + 1;
                }

            }
          
            IDictionaryEnumerator enumerator = sortList.GetEnumerator();
            richTextBox1.Clear();
            while (enumerator.MoveNext())
            {
                richTextBox1.AppendText("(" + enumerator.Key.ToString() + "): " + " " + enumerator.Value.ToString() + "\n");

            }
hope anyone can help me..