The only two people that I know of that voted for Reagan in 1984 and Obama in 2012 are my mom and my History professor that I had during the fall semester of 2012 and the spring semester of 2013. I am sure more people that I know did as well, but I never asked any of them about it.
A fair few old-school Northern Republicans fall into that category, probably.
I believe a survey a few years ago of the former members of the moderate-Republican Rippon Society in the 1960s that found that among surviving alumni, that a majority of them no longer identified as Republicans and IIRC a plurality of them were Democrats
