Here's a pretty good article about sore-loser laws:
It's only four states but they include two biggies: Texas and Ohio. The legal status is a bit murky, apparently.
Public perception of a sore loser is even harder to guage. There isn't enough historical record to go on. The example of John Anderson (1980) from the above article is not necessarily comparable to Ron Paul. However, it is encouraging to note the Anderson successfully got ballot access.