The latest IOS image version for the Cisco 3750 switch is 15.0(2)SE7. You can download this version from Cisco's website.
To download a Cisco 3750 switch IOS image for GNS3, follow these steps: Cisco 3750 Switch Ios Image Download For Gns3 UPD
Once you find the IOS image, click on the link to download it. You may be prompted to enter your account credentials. The latest IOS image version for the Cisco 3750 switch is 15
To download the IOS image, you need to create an account on Cisco's website. Go to https://cisco.com and create an account. Cisco 3750 Switch Ios Image Download For Gns3 UPD