If you have just picked up a used Cisco Catalyst 3750 for your home lab, or you are trying to revive an old stack in a production environment, you have likely hit the same wall: "Where do I actually get the IOS image?"
show version Look for the line: "System image file is 'flash:/c3750-...bin'" . If the switch boots, you already have the IOS. You can back it up via TFTP: cisco catalyst 3750 ios download
That is a scam. Either buy a switch that already has the version you need, or use the community repositories responsibly. If you have just picked up a used
Disclaimer: This post is for educational purposes. Always respect software licensing agreements. If you are deploying in a business, buy the support contract. buy the support contract.