Drop from Beastmen also can be stolen with THF. 4 Silver Beastcoins = 1 Silver ingot which is a free 6k if u farm this, and make them into silver ingots.
Easily farmed in Giddues from most of the second tier Yagudo, Mendicants and Persecutors. They can also be stolen from the third tier Yagudo, Priests, Theologists, and Votary. Cheap way to get silver if goldsmithing as well as a few NMs in the area as well.
if your using them on Silver Ingots it's not really worth it if you mine up Silver Ore and get synthesis support for 60gil you can make the synth (i got tired of farming Silver Beastcoins and decided to do this at about lvl 11 or 12 and it worked)