Follow the path north out of Bradtropolis past the dock, and once you cross the small bridge at the ocean corner take the path to the right.
Protip: It's a whole lot easier to bring a bucket of tadpole back home than leash a frog and pull it all the way back, but if you want a specific color you might have to. Wherever the tadpole 'grows up' will determine what color frog it is. Temperate=
orange cold=
green warm=
gray.