Just to bring this up to date as of Xcode 12.2, Apple is allowing Xcode to download the symbols.
1) Go to the Organizer and find the app you uploaded to the store.
2) Click the Download Debug Symbols button beneath Details.
3) Right-click the app and Show In Finder.
4) Right-click the xcarchive and Show Package Contents
5) Your dSYMs are in the folder...