: Large platforms like eBay and Amazon are the most reliable sources for finding legacy hardware from brands like Dell , HP , and Lenovo that still have Windows 7 installed.
: Sites like RefurbishedPC and PC Liquidation often carry stock of older business desktops (e.g., Dell OptiPlex series) that can be configured with Windows 7. Common Product Options
Most Windows 7 computers available now are refurbished business-class machines known for their longevity: How to purchase windows 7 - Microsoft Q&A