Beastmen don't actually drop gold beastcoins all that often, even with TH2 or more. Only one mob in Western Altepa does so, according to the quick wiki check I just did.
If you don't want to just buy the gold beastcoins off the AH, you have to be able to steal them. You can steal them from many coffer key dropping mobs, and I've also stolen them from the beastmen in WoTG areas. In the past, even a Yagudo Acolyte in West Saruta_S has gold.
As any THF will tell you, however, Steal is a rough proposition at best. You're best off going to a beastmen stronghold, farming the mobs for scrolls, and selling those in order to buy the gold beastcoins from the AH.
Frankly, my best source of gold beastcoins has been chocobo digging, but you're unlikely to get any by that method if you don't have digging leveled some.
Inia - Odin Server