I think I must agree when the problem is most severe a clean install is the only recourse -- but 221 people found Da Costa's answer to be helpful. And I think an upgrade/repair-install (as I posted on page 12) worth a try too.
There is an online Store...
https://www.microsoft.com/en-us/store/apps/windows
Microsoft Store Online -- or so it appears
Bit I can't find the Store app itself to be a download there.