I don't think so that fall calendar posted yet. Just sign up for their newsletter emails, and you will be notified once they post new performances. Or just keep checking their website. Anyways don't worry. You don't have to buy tickets way in advance. There are always tickets available to every opera unless you are planning to sit certain area. There are usually seats available in Orkestra. The best thing is to sign up to met emails.
You might have to move quickly if you want to attend a special performance, like a holiday gala - but apart from that you should be fine getting tickets even in the middle of the year. If you want to make sure you're on the early side, you could call them and see when individual tickets would be available. Season ticket holders and patrons get priority so some seats will be gone but there should still be a decent selection.
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