Original. It’s almost impossible to get original ideas for most normal people unless one is a Ph.D. and works on the edge of one specific field, or a rapidly growing field where an entrepreneur can form an “original” idea, or one just find a special need (idea) in daily life but everyone complains and ignores it and he converts to a product.
Variations. Often the so-called original ideas are either from ignorance (or blindspot) or the variation of existing ideas. No matter whether it’s from ignorance or variation, one needs to explore more on the existing ideas/or knowledge to remove the blind spot as much as possible and get inspired from the existing ones(standing on the shoulder of previous efforts!). When running out of ideas, maybe it’s a good time to explore and read more about existing “knowledge/or idea”, and maybe even challenge existing ideas (rebel the authority!). Yes, indeed, even the existing idea/knowledge could be derived from an incorrect method, incorrect data source, or at certain specific conditions IN THE PAST.
Conditions. Also, the condition matters, that’s why some old ideas could not work but it might become a great idea when the condition changes. An old idea can also so be great. What you think doesn't matter much(and is questionable), but the true conditions you’re in matter.
Seek truth. The truth about existing ideas, the truth about how to get existing ideas, and the truth about the current condition and future conditions.
How to get inspired? Read more, analyze more (against current conditions), and challenge more (Ask why and more why). Another approach is to work on a specific problem really deep, it seems obvious to you but it’s like an original idea from an outsider.
Are those above original ideas? Apparently, not, definitely not. It only means there is a lot to read if you think that’s original ideas, such as How To Think For Yourself and The Beginning of Infinity, you will know.
Stay humble and curious.