Another source for such high voltages .... again, becomming rare ... is the igniter transformer from an oil furnace.
HID ballasts can provide voltages anywhere between 600v and 1000v.
Then there is the case of "Mad Man Markum," who stole PoCo transformers, back-fed them, and created a Jacob's ladder arc that crossed his porch (about 6 ft.). Now there's some voltage!
