I doubt tickets are on sale yet. Most prem teams sell them about a month in advance, and pretty much always to season ticket holders first, then fan club members, then those who hold tickets to the previous game etc., then if any are left, they go on general sale.
If you have a visa card, try their concierge service. I scored tickets to the Champion's League Final a couple of years ago through them, and was privvy to witness Liverpool's miracle comeback. But they cost me a fortune, so unless you're prepared to pay through the nose, I wouldn't hold your breath if I were you.
Delivering Anecdotes of Dubious Relevance Since 1978