So, I am making buckled corsets right now (I make a corsets about every three years to remind myself why I DON'T), and was dismayed at how much buckles cost, through, say, Tandy Leather supply or even eBay. So I found that the best bet (for the nickle-plated that I am looking for) is actually
Tractor Supply Company (for those of us in the United States). I found these buckles 1 1/2" for 49c each(!) plus shipping, which is about 1/10 what they are other places. They are only available online, but after shipping, they still only come to, like, a dollar each. We'll see how they hold up, but they are pretty heavy right out of the box. Sadly, they don't appear to have brass...