If you're playing on the Forest Farm, Forageables will spawn in many places on the map, perhaps everywhere there's green map grass (not the grass you've planted). I don't remember if I've seen something up near the Shipping Box but I've seen them in every other location from the bottom right to the entire middle section and around Grandpa's Shrine.
The Forest Farm is my favorite because of those Forageables, honorable mention to the Beach Farm with its crates of fun things that occasionally wash up on your Farm shores. They're like receiving little gifts from the sea or the forest creatures every now 'n then and who doesn't like that?