There's an entire thread dedicated to get people together to do Cannon Defense to aquire rams, located right
here. However, it looks as though it only goes on during Friday and Saturday nights, because they permit the game to go on longer.
The Revenant Cannon Ram is very rare and strong, and would most likely take longer than most games of CD to aquire (past Wave 30, I'm guessing.) As such, I doubt a lot of people can stay up late on weekdays for a game of CD. So, I suggest waiting until one of those CD groups are available.
As for plundering it, it looks like there's even less of a chance then, so I really suggest just waiting to do CD.