[Rumil]

One source of cash, or precious metal, for the Shire must have been derived from their dealings with the Dwarves.

The Dwarves often travelled through the Shire and seem to have bought agricultural produce from the hobbits, probably sometimes by barter for 'ironmongery' of various types, but conceivably with coins. The Dwarves were not farmers and had a similar sort of relationship with the men of the second age. I seem to remember this from UT where Gandalf explains his dealings with Thorin and 'of Dwarves and men'.