I would say that somewhere in the top five questions an author is asked is the perennial favorite, "Where do you get your ideas?" Huh. Must I confess? I have no idea.
I write using the seat of the pants method. The two times I've attempted to outline books prior to writing, neither of the books bore even the faintest of resemblances to the outlines. So how do I manage it? Free association? No actually, I allow my mind to explore all the possibilities of what if.
What if the people were blue? What if King Arthur never died, but went to his home planet, Avalon instead? What if angels could shift into any animal they wanted to? What if.
Sometimes, our brain is trying to let us know that there's a great story lurking inside, but our control knobs won't let us go. Then that story dies, because we've strangled it. Nearly every time I have trouble with a story, it has to do with that very issue. Instead of letting my brain present all the possibilities... I try to squeeze it into a story girdle, trying to prevent any of the jiggles and wiggles that might possibly make it interesting.
Inspiration? That's the what if. What if I turned right instead of left? What if my character crochets while he watches football? What if my heroine loves to do woodwork or plumbing? When I as the writer open myself to new possibilities, I discover the story lurking in the shadows, just waiting for me to set it free.
What if a dragon and a tiger fell in love? Hmmm. See? Infinite possibilities. With all those possibilities, the only real problem is finding the time to write all the stories.