You might find "New Old Stock" (physical DVDs) on sites like eBay or through specialty software liquidators, but be extremely cautious of "too good to be true" digital-only deals, as these are often illegitimate or contain malware.
You used to be able to download official ISOs from the Microsoft Software Download page if you had a valid product key, but this service is largely retired. buy windows 7 iso
Microsoft officially ended support for Windows 7 in 2020, meaning they no longer sell it directly. You might find "New Old Stock" (physical DVDs)