like the post above says, I buy all the ore, ingots, and leather from the merchants. Got my smithing up to 100 no problem. A good place to buy and create is whiterun since there are 3 BS's there that sell the materials.
There's a mine close to Markath (don't remember exactly the name or it's location, but you can recognize it because there's a little house very close to it, and a smelter in the exit of the mine) which has TONS of gold ore. Got about 29 ingots when I finished looting it.