Places I have found flint (not very big pieces, but enough to strike a spark from an old file or to knap down to a small knife /arrowhead size):
1. Among the bags of shells and stones that the children have brought back from holidays.
2. In among the gravel on my front driveway.
3. In the hardcore of a local untarmacced road.
4. In among building rubble at my brother's house.
For myself, I need to switch into observational mode when I go for a walk and it is amazing how many resources I can find if I'm really looking. It's not so much going out looking for a piece of flint, it's more a case of saying - "oh there's a piece of flint - that might be useful - or there's some birch bark". Mind you, my family find it amusing when I come home with a pocket full of cramp balls, or dry grass.
Having said that I doubt very much if I am going to find a nice big flint nodule where I go walking, but it could be argued that bushcraft is about using what you have available locally.
Geoff