Cheapest way to get these discretes into your Harmony is to ask Logitech to add them.  Send them the Pronto Hex codes in this thread for the discrete codes in question.  If they aren't willing to do that, see post #21 of the linked thread.  Buy a Comcast remote from eBay, and follow the instructions in post 21 to make the Comcast send the desired IR signals.  You can teach those to the Harmony. Some other cable company remotes will also work.