Any advanced morai skill (including venomancers) can be found in a universe chest, which can be obtained by doing Endless Universe or buying from the boutique. These chests, when opened, have a random chance of giving you any advanced morai skill (not just the one for your class) or an item.
Generally, each class has only one advanced morai skill, (wizards might have two, not sure on this though) and then another morai skill that cannot be gained by any order but needs to be obtained by the universe chest.
And no, venomancers can only turn someone into a puffbird.
Hope this helps.