Nowhere near you but blackthorn bushes (the source of sloes) were used extensively by farmers in England for cattle enclosures around their fields so my advice is to find a local area where they still use hedges around fields rather than wire fences or stone walls.
I think that the best way to search out foraging sources is on a pushbike. You are going slow enough to check out the hedgerows and fast enough to cover a lot of distance in a day.
After riding around our local area we can now source any amount of apples, crab-apples, sloes, blackberries, rose hips and plums when they are in season; and the joy of it is that they are all free!! :thumb: :thumb: