and btw they don't only grow on cow shit..?? dunno were you heard that.
you won't need to find a farm. look for wet, grassy, muddy, dank areas. like in a forest, or Mesh Gear Fox's Y-fronts.
Psylocibes cubensis, the magic mushroom that lives in my area, only grows on cow manure, horse manure, and manure enriched soil. I heard that from reading field guides.
Although that is a cliched and partly wrong statement, that they only grow in cow dung, it's a good rule to follow when you're searching
They also grow in damp vegetative areas with rich soil
But if you're in an area with cows it tends to have that quality anyway because of the dung, even if they're not growing DIRECTLY out of the shit.
So go to some cow fields.