If you are unable to locate CM Mobile via the Play Store, this is likely due to the 'country' settings within your Play Store Account. Your Play Store account must be set to the United Kingdom otherwise you will not be able to install this.
To change your country, do the following:
On your Android device, open the Google Play Store app.
At the top right, tap the profile icon.
Tap Settings > General > Account and device preferences > Country and profiles.
Tap the country where you want to add an account.
Follow the on-screen instructions to add a payment method for that country.