Single Game Ticket Question…

Hey! Long story short I'm gonna be in Houston during July and I want to go to an Astros game, but checking in the MLB Astros tickets page, there aren't any July games available to buy, neither August and September… The last one available is June 26 against the Rockies, So I was wondering, do they block the tickets for 1 month+? Do I need to wait until June so the July tickets are available? Saw other teams but Astros is the only one that has this case, hopefully someone can help me, and thanks in advance!!