There might legitimately be no one. Breckinridge got only a couple thousand votes in each Northern state, and these people were probably Buchanan voters. Fremont wasn’t even on the ballot in the vast majority of the South, except for a few border states where he got around 200 votes.
There were a good amount of Buchanan-Lincoln counties in the Midwest, but nothing for Fremont-Breckinridge. If any voters fall under this category it’s less than 100 at most.
The only possible thing I could come up with is someone who voted for Fremont in 1856 and then for a Democratic fusion with Breckinridge in 1860. There were probably some of these in New York, which swung D. But even then that doesn’t really count since most of the electors on the slate were for Douglas and there were still more electors for Bell.
