hifi-remote.com has upgrades for DVP-C600D and DVP-C670D, so we know which IR signals these use. It is a near certainty that the C650D has the same IR codes.
Probably cheapest is a
Comcast DVR remote. Use setup code 20533.
Or get an Atlas cable remote using DVR 0533. Similar prices.
If you want to splurge, get the learning 5 device RCA RCRP05B. Also 0533.