Most authors can’t go to a party without someone coming up to them and saying “I got this great idea for a book. Why don’t you write it and we’ll split the profits?” Polite writers say “No, thanks.” Impolite writers laugh.
Many people think the idea for a story is the most important part. It’s not. Anyone can come up with an idea that could make a good story, but the matter of execution is something else entirely. A writer has no trouble coming up with ideas and doesn’t need help. It’s the writing skill that turns the idea into a story, and the idea is only about 2% of that.
If you think it’s really a great idea, then write the story yourself. You may be better than you think, and you have nothing to lose.