All the vendors start with a set amount of gold, and do not get more unless you buy things from them. This should still leave you plenty of gold to sell excess loot, increase level caps, etc, and unlearn skills up to 3 or maybe 4 times. If you use the battle tower runners too much to farm diamonds, malachite ore and maybe plants to make potions to sell, merchants may run out of gold before you run out of excess loot, though.
There are a couple merchants in Aleroth with a fair amount of gold, if you have not been there yet. Other than that, check out the merchants in the bunker, dragon cliff castle, High Hall and the harbour. If you have not cleared the path yet between the depleted ore mine and the harbour / High Hall, you can meet a traveling merchant there once, with some gold and at least a malachite gem to buy.
