Some Tumblr blogs are dedicated to Harry Potter fanfictions. You could search for relevant tags such as '#MinervaHermioneMarriedFanfic'. There may be users who share or recommend great fanfictions on this topic. Also, join some Harry Potter fanfiction groups on social media platforms and ask for recommendations from fellow fans.
Fanfiction.net is also a great place to look. It has a large collection of fanfictions. However, the quality may vary. You might need to sift through some stories to find the really good ones about Minerva and Hermione getting married. Check the reviews and ratings if available to help you choose.