You can grab Pillow Pets from liquidators, especially ones who service Walgreens, CVS or Rite Aid, all three of whom tend to put up and take down a PP display with the season. My daughter just got her sixth one; it's ridiculous lol I've never purchased a liquidation load of them, but if I had to make an educated guess I'd say that they are probably pretty severely cherry-picked in advance.
One thing you might think about is a local retail source, which happens to have the harder-to-find/higher demand items. Like many similar kids' items, there are sellers on Amazon and eBay selling these ~$20-30 items for greatly more money, because it can be hard to get them from the source. I know this from experience: The one we just got, literally received it a few days ago from MPP, we ordered in November. It took more than three months for them to get it back in stock! Kids are very particular, and parents are very gullible; if the market will support taking an offline retail item and selling it online for 2x retail or more, it might be worth doing a little research.