If I play Repeat Ball and choose a Pokemon that already has 2 in play and 2 in the discard pile, can I still search my deck for that Pokemon and fail?

You cannot search your deck since it is public knowledge that you won't find one because all four copies of the card are in known areas. If you have another valid target in play you must choose one of them; however, if you don't have a valid target the Repeat Ball goes back to your hand.

Relevant cards