Right now the only way to farm for Diamonds is via the Nulgath Larvae Quest or the Supplies to Spin the Wheel quest. Diamonds are both a pretty rare drop in both of those quests.
People have also been talking about farming Diamonds using Klunk's Quests, which are rare now, but accessing them by using a quest loader. I haven't tested it out yet but I don't really think its going to work.
Anways your best bet is going to be using the "Mana Golem" Bot or the "Supplies to Spin the Wheel" Bot, which can both be found in the bottom Bot menu in Le Bot 7.6.