One charm is dropped at a time

　　King Black Dragon (level 276) Although this method of gaining charms is not reccomeneded, as KBD is going to be slow to obtain  RS Gold charms obviously..it takes a while to kill a KBD (depends on your level) however the time could be worthwhile because of the special drops it has, such as a visage.

　　Green Charm droppers:Bloodvelds (level 76) These creatures, do not drop charms as often as waterfiends and also the rock lobsters, but are among the best choices to obtain green charms. One charm is dropped at a time. Bloodvelds, are simple enough to kill and employ a melee based magic attack meaning wearing armour that gives good magic defense (eg. black d'hide body, chaps etc.).

　　They may be found at the Canifis Slayer Tower, God Wars Dungeon (only 1). Their are probably more locations where you'll find these monsters but?-Canifis Slayer Tower will be the best spot to kill them.Green Dragons drop 1 charm at any given time and are quite easy to kill.