It must have been more common back in the day
(1896: Bryan ran on Democrat and Populist lines - as far as I could figure it was quite a few states).
Explanation from Wikipedia:
Electoral fusion was once widespread in the United States. In the late nineteenth century, however, as minor political parties such as the Populist Party became increasingly successful in using fusion, state legislatures enacted bans against it. One Republican Minnesota state legislator was clear about what his party was trying to do: “We don’t propose to allow the Democrats to make allies of the Populists, Prohibitionists, or any other party, and get up combination tickets against us. We can whip them single-handed, but don’t intend to fight all creation.”[3] The birth of the Minnesota Democratic-Farmer-Labor Party made this particular tactical position obsolete. By 1907 the practice had been banned in 18 states; today, fusion as conventionally practiced remains legal in only eight states, namely:
California (Presidential elections only)
Connecticut
Delaware
Idaho
Mississippi
New York
Oregon
South Carolina
Vermont