PD & DAs get lots of trial experience. Another good way is to work for a municipal tort claims department- cities get sued a lot, so heavy caseloads and lots of litigation. JAG isn't a bad move either- great training and experience.
Of course, all of them don't pay too well.
Smaller PI firms seemed to be looking for people they could work with instead of stellar academics (or at least the ones that I interviewed at)
However, I'd recommend working for a trial lawyer before deciding that's what you want to do. Trial work can be boring.