Since the details are scarce, Gary could be anyone. He might be an ordinary person living an extraordinary life as a gay man. Maybe he is a local figure in a community known for his contributions, or perhaps he is just a character in a story that is meant to represent certain aspects of the gay experience.
It could be just a random chant or repetition that someone has associated with the movie for no particular reason. Maybe it was part of a joke or a personal mnemonic device to remember something about 'Pulp Fiction'.
One of the great Norman Osborn stories is in 'The Amazing Spider - Man' where his transformation into the Green Goblin is explored in depth. It shows his descent into madness and his complex relationship with Spider - Man.
In the 'kid a gary carter story', Gary Carter might be a local figure. Maybe he was a shop owner who was always friendly to the kid. Or perhaps he was an old-timer in the neighborhood who had many interesting stories to tell, and the kid was always drawn to him, and that's how their story began.
Yes, there are many 'Harry Osborn' fanfics. You can find them on various fanfic websites like Archive of Our Own. There are different genres and themes related to his character, from friendship stories within the Spider - Man universe to his own adventures.