Specifically, following the "Download" link on Extension:SimpleCalendar takes me to a page saying "no such extension" (Special:ExtensionDistributor/SimpleCalendar), and presents a form to choose an extension. Selecting any extension in the pull down box adds another form to download for the current version. Submitting this form does nothing.
Topic on Project:Village Pump
I've fixed the download link. It's not hosted on WMF code repository
I can access the individual files now. Thanks.