No instance size with 8 vCPUs and 128 GiB RAM for Windows Server and SQL Server on Amazon EC2

You could choose an instance size that is a 128gb and change the cpu on launch to match the number of vcpu you require.

https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/instance-specify-cpu-options.html

You can specify these CPU options during instance launch. There is no additional or reduced charge for specifying CPU options. You're charged the same as instances that are launched with default CPU options.

This may not be what you’re looking for cost wise. Have you considered RDS?

Have you considered x2iedn.xlarge ? It has the memory you are looking for.

SQL Server is much more memory and IO intensive than CPU. Check out a guide we just published https://aws.amazon.com/blogs/modernizing-with-aws/a-guide-to-optimizing-microsoft-licensing-on-aws/ and look for Use the Optimize CPU feature for SQL Server workloads.