Another option is to check out dedicated Marvel fan communities on social media platforms like Reddit. There are often threads where fans share and discuss their favorite fanfictions. Just post a request asking for Peter Parker and Jean Grey married fanfictions, and someone might be able to point you in the right direction.
You can try searching on fanfiction websites like Archive of Our Own (AO3) or FanFiction.net. These platforms have a vast collection of fanfictions, and by using the relevant tags such as 'Peter Parker', 'Jean Grey', and'marriage', you might be able to find some interesting stories.