Thaumaturgy is not readily available to any of the clans in the game.
The Tremere antitribu were recently wiped out by mysterious powers. However, they did pass on their knowledge to the Sabbat before that happened.
As such, you may take the "Additional Discipline (+5)" merit to gain Thaumaturgy to count as a clan discipline.
You start with a Primary Path rating equal to your Discipline rating. Other paths may be purchased at a rate of 4 freebies per dot. You also start with one ritual per level of your Discipline, additional rituals may be purchased at a freebie cost of 1/2 the level, rounded up.