The updated info for creating a Visual Studio for Mac support incident is to go to Technical Support > Product: Visual Studio > Assisted Support on and then select Visual Studio Community/Professional/Enterprise 2017 for Mac. If you do need to get an older version of Visual Studio for Mac itself, the best option at this time is still to create a support incident to request the version you'd like. In many cases, the latest version of Visual Studio for Mac will be backwards compatible with previous versions of the Xamarin SDKs, so you can in many cases just install those earlier Xamarin SDK versions over the current versions and leave Visual Studio for Mac and Mono Framework MDK at the latest. I have now updated the 15.7 Release Xamarin Release Blog post to provide the links to those locations. And the Mono Framework MDK is similarly available in the Mono Project download archive. As an update on this topic, all of the recent previous Xamarin.iOS, Xamarin.Android, and Xamarin.Mac packages are available in the archives on the open source continuous builds server (under the Xamarin.Android and Xamarin.MaciOS tabs).
