Hey there! The event just started, you haven't missed anything yet!
Are you referring to the fish items? Those can be obtained by loosing a hamster race at the race track. The race winners are determined by chance so you will just have to be (un?)lucky to get some ^^
Just adding on to what Burrito Bunny said, if you pick the winner of the race, you get the hamster you picked along with a first place trophy item. If you pick the second place winner, you get a second place trophy and three random fish items. If you get third, you get a third place trophy and two random fish items.