Basketball Reference is definitely the go-to place for that information. Beyond that, it's just a matter of going through every team in the game, which is why I thought it might be better as a community project a few of us could contribute to.

You're definitely right, you have to double-check the transactions. In fact, if there's something I wish B-R would add, it would be final season-by-season rosters so that you could tell that at a glance.