So I'm assuming your input is 240VAC, right?
I'm not sure if it's even possible to get 10% THD with a buck with that output voltage. Simulation would tell easily... But if possible, I would try to use a topology using a transformer, like a flyback, forward, or pushpull. I've seen Sepic used for PFC as well. Then you won't have a problem with dead conduction angle on the input and you can get good THD.
Sorry if it sounds like I'm dodging the question, but buck PFCs are really sort of awful so you should make sure you have no other choice.