I've struck out with the local plant / tree shops when asking to purchase poplar or willow cuttings. Not sure why they don't want to do it, but they don't.
Anyone coming after, I struck out locally and had to punt to Amazon.
I bought these: https://www.amazon.com/gp/product/B075PD1YHW and had good luck with them. I planted some of the sprigs, and the rest appear to be happily pumping out willow water.