there is a website called pixabay where you can found over 700k FREE (for commercial use too) HD wallpapers of every categories,
some examples:
https://pixabay.com/en/gleise-old-railroad-tracks-seemed-1555348/
https://pixabay.com/en/coins-currency-investment-insurance-1523383/
https://pixabay.com/en/coffee-cup-still-life-3d-blender-777612/
if you want I can download some wallpapers and then, I will send them to you, or you can just download wallpapers you like