You could just store each flipbook reference in an array, then do a random integer from 0 to the array’s length(just in case you ever add more flipbooks). When the actor spawns it would then just be assigned which ever of the flipbooks is chosen from this array. I did a similar thing to assign random materials when spawning a bunch of asteroids.
At the moment I have an enemy character that spawns in the game (actor) at random intervals, I want the enemy to spawn in with one of three random animations (or flipbooks as this is a 2d game). The flipbooks are just slight variations in the way the enemy looks, just so there is variation in the game, they have no other properties other than just looks. I want to be able to do this without using 3 different actor classes for each animation if that is possible.