You don't need MSDN subscription to get it, here's a direct download link: https://www.microsoft.com/en-us/download/details.aspx?id=55849
BUT! As mentioned in the description, MFA server is no more:
As of July 1, 2019, Microsoft will no longer offer MFA Server for new deployments. New customers who would like to require multi-factor authentication from their users should use cloud-based Azure Multi-Factor Authentication. Existing customers who have activated MFA Server prior to July 1 will be able to download the latest version, future updates and generate activation credentials as usual.