I know that there are a few left-handed 870s. (A buddy's dad just picked one up absolutely dirt-stinking-cheap.) I also used to dove hunt with an Ithaca that was a bottom-eject model. I think it was Ithaca Model 37 Featherlight, but the one I hunted with was a 20 guage. It was a sweet shooter, too.
They still make 'em, though: http://www.ithacagun.com/featherlight.html