Ebay. Picked up a set for our 89' BII for about $70ish. Complete units, brand new in box.
(that's about $70ish for both!)
In most cases you'll spend about 2-3 times that amount just to replace the lenses alone. If yours have the yellowing dingy look, you might get away with the 'restoring' kit, but if it's to far gone? Easier just to replace the whole thing and throw a shop a few bucks to align the headlights.