Typically they're on the frequencies known as brown dot, blue dot, etc. That's where I would start my search and I imagine would be most likely to get what you want. Wish I could give you more help to the specific cities but I have not checked Fresno or Madera in person. Though it is highly unlikely that Walmart would be on these radios I would give the FRS/GMRS frequencies a look as well.
Wal-mart in douglas county, nv uses (f1)-154.5700/csq (managers/security)
(f2)-154.6000/csq (never used that i know of) frs/gmrs 462.6000/csq (stockers/
parking lot [cart retrival] misc depts.