Hello I will help you with your question,
This vehicle does have keyless entry installed and the remotes are lost?
To add a remote to the Keyless Entry system on your vehicle will require a Tech 2 scantool so you will have to find an ACDelco shop or a good independent shop that has the tool. Of course the dealer will have a Tech 2 also.
Here are the instructions even though you do not have the tool yet
Programming RKE Transmitters With RCDLR Module IMPORTANT: All key fobs must be programmed each time any one fob is programmed.The scan tool must stay connected until all of the transmitters are programmed.
Let me know if you have further questions about this