I think itd be easy enough to get them from a friend of your parents. I don't know how you can consider it "hard"? I have many dentists in my family, just none where I am going to school. I shadowed a brother of my girlfriend's roommate's friend.....doesn't get too much more weird than that...I had never met the guy until I showed up at his office the first day. I mean, I had called him to confirm, but prior to that the whole conversation had worked its way through his sister(and sometimes his sisters friend....or even worse through my girlfriend to her roommate to his sister and then to him).
Point of what im trying to say is, if finding another dentist (in the town your family works in) is "hard" then take a good look at what you are trying to take on here being pre dental. As for my opinion, I'd rather get the shadowing hours from a non relative. I think some people might read something into it when its your parents signing off on the shadowing. Like, maybe this guy isnt motivated enough to do this for himself. Maybe its his parents shoving him down this pre dental path. Maybe im overanalyzing it 🙂 *shrug*