We got ours from a larger farm nearby a few years ago - they had purchased a soy based fertilizer and the distributor didn’t have any return/recycle incentives so the farmer was selling them on the cheap. I think we found the guy through the farm & garden craigslist section but I can’t really speak to how reliable that is anymore. If you’ve got a winter farmers market around you it might be worth asking around there (I’m loathe to suggest fb marketplace but if you’re already there that might be convenient as well)