Options now
You can check the seat exchange board now and in the next week to see if any with a seat need to sell
You can keep checking the forum for news of any more seats that might go on sale via William Hill, a possibility.
You can turn up at the venue for midday Saturday and buy a seat if any remain (we don"t know yet, obviously) or go on the first come first served alternates list. Usually up to 10 alternates get in via exits in the first two levels