Unfortunately, bulk buying licenses is only available is only available in U.S. and Canada currently. Hopefully soon we will have access to this convenient service! As stated by Google:
Buy and manage app licenses
To get paid apps for your users, you buy apps that support bulk licenses in managed Google Play. Each user that uses the app needs a license. When you buy an app, start with the number of licenses you think you'll need. You can always buy more licenses later if you run out.
You purchase and manage app licenses by signing in to managed Google Play. However, to assign (or unassign) licenses to users, you must use your enterprise mobility management (EMM) console.
Approving licensed apps
After you purchase an app, it’s approved and made available to users in your organization.
If you don't want new users to install an approved app, remove it from the approved list. People who haven’t installed it can no longer see it in managed Google Play. However, users who already installed it can keep using it.
Who can buy apps?
Buying apps that support bulk licenses is currently available to customers in the U.S. and Canada.
You must be a registered managed Google Play administrator. Your administrator account also must have a Google Account with an associated payment card.
Find apps to purchase
Go to managed Google Play.
Next to a section, click See more to see a larger selection of apps.
If you still don’t see the app you’re looking for, use the search box at the top of the page.
After you search for an app, from the All prices list, select Paid to see the apps that support bulk license purchasing.
Buy an app
Use your Google administrator account to sign in to managed Google Play.
Select the app you want to purchase and click Approve.
If you see an error, it might mean that the administrator who manages your account has turned off Google payment services for your organization. Or, you haven't set up a payment option for your administrator account.
To accept the app permissions on behalf of your company, click Approve.
Choose how you'd like to handle new app permission requests and click Save.
Enter the number of licenses you'd like to purchase and select a payment method.
You can purchase more licenses later, if needed.
To complete the purchase, click OK.
See app licenses and purchase history
Sign in to managed Google Play.
From the Apps menu, select My company apps. The number of remaining licenses for each app is shown under Remaining.
To see the purchase history, click History.
You can also click an app to see:
The number of licenses that you bought:
The available licenses:
Purchase more licenses for an app
If your users try to install an app with no available licenses, they're prompted to contact an administrator for help.
Sign in to managed Google Play.
From the Apps menu, select My company apps.
From the All apps list, select Paid.
Select the app and click Buy.
Enter the number of additional licenses you want to buy and verify the price.
Select a payment method and click Buy.
If the app is on your approved list, the new licences are immediately available. If the app is unapproved, you’re prompted to re-approve it for the licenses to be available.