Special:ExtensionDistributor on this wiki currently just says "Unable to fetch extension list!". Possibly related: https://phabricator.wikimedia.org/T188692
Topic on Project:Village Pump
This is probably due to the current Gerrit outage, see https://lists.wikimedia.org/pipermail/wikitech-l/2019-March/091744.html
In the mean time you should be able to get copies of extensions via searching Phabricator Diffusion e.g. https://phabricator.wikimedia.org/diffusion/query/Fc8MaJ6GJOrD/#R