Having failed to find a list of fictional characters in books who are left handed, I decided to look for actors, and that turned out to be a bit more productive.
Bruce Boxleitner (Sheridan in Babylon 5) is indeed left handed.
Over in the Star Trek universe, there are three members of the TNG crew who are played by left handed actors - Wesley Crusher/Wil Wheaton, Data/Brent Spiner and Worf/Michael Dorn.
In that galaxy far, far away, Mark Hamill is left handed, but I don't think that carries over to Luke Skywalker (I honestly don't remember which of his hands got chopped off - but it didn't seem to make much difference, artificial hands in that universe being pretty much indistinguishable from real ones). I've also seen it alleged that all the Stormtroopers are left handed - something to do with the way their armour and blasters were designed? It's not something that I've ever noticed myself, but I will be looking out for that next time I sit down to watch Star Wars.
Ron Perlman is left handed - so maybe Hellboy is too? And Vincent from Beauty and the Beast?
Peter Graves, the leader of the Mission: Impossible team in the 1960s, is left handed, and so is Martin Freeman (though Watson seems to be right handed, and I'm not sure about Bilbo Baggins).
Moving on to archers, Jeremy Renner (Hawkeye in Avengers Assemble) and Jennifer Lawrence (Katniss Everdeen) are both left handed.
Angelina Jolie is left handed too, which presumably covers Lara Croft.
And, coming back to Game of Thrones (mentioned in the last post I was talking about lefthanders) Arya Stark is described as left handed in the books, but Maisie Williams is right handed, so she learned to swordfight left handed on screen.