The AWS Serverless Application Repository (SAR) is now available in the AWS GovCloud (US-East) Region. This increases the availability of the service to a total of 18 AWS regions across Asia Pacific, North America, EU and South America. To see the complete list of where SAR is available today, please visit the AWS region table

from Recent Announcements https://aws.amazon.com/about-aws/whats-new/2019/09/aws-serverless-application-repository-now-available-aws-govcloud-region/