Furi

Firstly, it's best to do this in practice against The Chain.
Secondly, you want to parry as late as possible. After 20 parries in a row with no perfects, i decided to delay my previous timing by maybe 1/3 of a second, and i got 2 perfects out of 5. So take your regular parry timing, and simply keep delaying it little by little until you start getting more. Also, i recommend starting the chain fight, hurting him enough to when you're in the hand to hand combat ring, and doing it there, as there's no distractions or other moves he can use