Assuming you still have access to the app in iTunes Connect, it's now possible to download the dSYM from iTunes Connect, too. Login, go to My Apps, select your app, then tap on the Activity tab at the top. Tap on the relevant build, and, assuming the app was submitted with symbols in the first place, you should see the option to "Download dSYM."
The file you get is called dSYMs (without an extension) but it is in fact a zip file. Add the .zip extension, unzip, and you'll find your dSYM(s) inside.
(I needed to do this this week since Crashlytics was complaining about a missing dSYM: https://stackoverflow.com/a/35374388/2397068.)