Normally, all badminton shops have them and they should be able to give you a couple for free as Yonex supplies grommets to all authorized dealers for free.
Thanks for the infor BlueJeff. If I wanted to replace like the whole set on the racket I think they would charge me - In that case, I would rahter buy the set at my own expense to replace them myself. I emailed to Yonex US and I'll see what they.