I normally stock up in Canada at local Toyota dealer. But I have also bought in bulk on Ebay. For example: current item # 220697378247 which fits many applications on the BJ71. BTW, my BJ71 is 24v but runs standard 12volt headlamps.
Hey 1978HJ45 I converted those headlights to H4 bulbs and housings that I puchased from 4 wheel auto. I can give you the part #'s when I get home on wendesday if you like. On my BJ74 I am using an even higher wattage bulb that are even brighter then the ones in your 71. And yes the rest of the truck requires 24v bulbs as well.
ps: if you are in the market for new lenses, go for the euro (ece) units. waaay crisper, throw farther, and they throw a beam towards the shoulder of the road. just keep your dot approved originals under the bench for a rainy day, as you might not pass an inspection without them.