Good question. Honestly, there are a few places you could look. You could look online, or you could buy a book of novel (not the book, but the adjective) suggestions and prompts. That, is what I did. Well, I should clarify the fact that my father bought me the book for christmas. It was a great present and there are so many ideas that have helped me and inspired me.
So, all in all, I greatly support the use of writing prompts. Don't be ashamed of having to borrow someone else's prompt to create a new and invigorating novel! Be grateful that someone is allowing it.
That's all I've got,
write on.