You can use the pname: prefix to search for apps on the Play Store by package name, e.g. by typing "pname:com.google.android.gm" into the search box.

Unfortunately it doesn't always work. In particular it doesn't work for:
– recently created apps that aren't yet indexed
– purchased/installed apps unpublished by the developer
– incompatible or country-restricted apps

Pname+ can still access the Play Store listing in such scenarios.

Source code is available at https://github.com/bndeff/pname