Instead of looking for so called callouts on the web, you will have most of the maps in a single application. More functionality will be added within a certain time, but at the moment you can view the maps. Bombtimer 40 or 35 seconds. The app is NOT fully optimized for landscape mode so it may not show everything correctly. This will probobly be fixed in some time.
Davvarn is the official developer of the app that can be found in the Entertainment category. Over 100K users downloaded and installed Maps for CS:GO and its most recent release was on May 20, 2016. According to the latest info, this application is rated 4 on Google Play.
There are ads in the app. Get the free .apk setup package of Maps for CS:GO 2.3 and check out users' reviews on Droid Informer. This installer occupies 12 MB on disk and it runs on Android devices 4.1 and higher. The security report shows that the app is safe.