It's based on luck, I think - or at least personally believe. But I got my first how to chicken on my first 5 tries, got my second (and last) chicken after 14-18 tries. It wasn't super rare on my end, but it could've been on others.
Though I hope you got lucky somewhere along the event and got it.
-- Not related, but I cannot see my Hot Chocolate Bar(s)
When I opened the game after the event had ended, it appeared invisible (and still does) I thought I somehow managed to lose them to server until I tried placing my mayflowers back out.
Is it like this for anyone else who had bought the Chocolate Bar as well?