My starting point is equilter.com and they offer half yard cuts.
They don't have many options right now, but for stash building I always look at their scrap packs.
https://www.equilter.com/category/38...se-scrap-packs
Sometimes they have a theme that matches exactly what I want, my black and white bundle was particularly excellent. They are the miscellaneous bolt ends, so usually a sloping cut across the full width of yardage .
My usual 2nd stop nowadays is Fields, a small chain in Michigan. I'm not exactly sure from the website if they are fufilling orders right now, but it looks like they will cut down to a quarter yard!
https://shop.fieldsfabrics.com/