where to find the best sources of mana

[Tianna]

My Endless Feast building (evolved 7x) makes 46480 mana every 24 hours. It is by far the best mana maker I have in my city.

 

[Dhurrin]

In the spring there usually is the Phoenix event and that event tends to have some really nice mana-producing buildings from before that come back as daily prizes.
The Lava Egg, Galactic Phoenix Egg and Burning Pool are really good sources. The Somnial Pool is even better, but is not offered as often.
From other events the Manta Ray, Aqua Weaver and Magical Nutcracker are good too.
And several of the evolving buildings do very well in providing mana.

And don't forget about the AWs; the Dragon Abbey basically delivers mana on demand when you use enchantments, the Maze of Dark Matter reduces decay (allowing for larger stores) and produces a decent if not huge amount every 3 hours and Einar's Embassy can produce pretty massive amounts once a week for those who do well in the tourney.

 

[Dhurrin]

Moonstone gate, mana plant, gum tree combination are by far the best per square for mana. You need all three touching to max them out. They can be won fairly frequently in the Spire. My mana plants (I'm in Elementals) are giving 3300 mana on one square per 18 hours, essentially per day. Should give well over 1000 in Woodelves. Of course the gum tree will later give, well, gum, and the Moonstone gate, well, moonstone, but by then you'll have Dragon Abbey. They are also easy and desirable to upgrade at 1 RR.

Define 'fairly frequently'. I have/had multiple testcities that after 2 years still did not have the set complete