Tinker's Construct adds oreberries, which you've surely seen in caves while spelunking.
A fully-grown berry bush will return one berry of the appropriate type upon a right-click. Bushes will also spawn more bushes near themselves from time to time, so berries are totally and completely renewable.
There are bushes for iron, gold, tin, copper, and aluminum. The fruits of each of these bushes also happen to be equivalent to nuggets of the appropriate metal.
If I'm not mistaken, oreberry bushes need darkness to grow. So find a cave and throw some Aluminum oreberry bushes on the walls, and you'll eventually have an unlimited supply of aluminum.
Also, I'm not sure if MFR harvesters work on oreberries, although I wouldn't be surprised if they did. I also don't know if they left-click and return the block, or if they just right-click and give the berries. If it breaks the bushes themselves, I'd recommend messing with its settings or trying the Fruit Picker.