It hasn’t been shown on Cartoon Network since the series ended. To make things more complicated, there were two seasons of Justice League followed by at least two (possibly three) seasons of Justice League Unlimited, where they greatly expanded the cast of superheroes. I think everything is out on DVD at this point, but I didn’t know it was shown on TV whatsoever anymore.
The DVDs are a wee bit screwy. All of Justice League is available. The first 2 seasons of JLU are available as well, but they call the 26 episodes 1 season not 2. It has the entire Cadmus story line and ends with, fittingly enough, Epilogue. I don;'t know what they plan on doing with the 3rd season episodes.