Sure there are plenty of other enemies you can do this against, particularly earlier enemies in the first dungeon, however I got this on the Glorious Hand in Magatsu Inaba.
The hand went and used Rage on himself, which allows you to do double the damage. Either add some attacking boosts, or something like Mind Charge, and use your strongest moves, (in my case it was Megidolaon). This should easily see you pass 1K damage, and you can do this whilst just going through the latter dungeons if you wish, than having to go back.