Like Pam said above, get a list of providers from your Dad's health insurance provider.... then go on the Internet and research out each and every one... look at their resumes, location of office [you don't want to be across town because one's parents tend to go to the doctors' offices quite a bit, closer the better]... then make an appointment to introduce yourself and your Dad.... if the office is bright and cheery, the Staff is all smiles, and the doctor knows what he/she is talking about and has a good bedside manner, then you have a winner :)
To find doctors that are highly rated, check out the website healthgrades. Also, check with seniors in the community, church, wherever you may meet and talk to them and ask.
I went to my local hospital with a list of approved providers and asked nurses at the nursing station who they would recommend for their elderly parents. I found a good gerontologist and then he recommended all of the other types of physicians (cardiologist, orthopod, etc.). They may be reluctant at first, but once one started talking to me, I got lots of good info. The other suggestions are also good!