Trying to access number inventory via API

Hi.

I am working on an internal tool for my company to be able to onboard employees into ringcentral. I am able to create the users, but now I want to be able to assign them a number from the number inventory. 

I am able to successfully make the calls to reassign numbers but was wondering if there was a way to access the phone numbers in the inventory via the API? I want grab this data to be able to parse for specific area codes and then use the ids in the call to reassign numbers.

All I see in the documentation is a way to get the phone numbers attached to an extension. Is the number inventory an extension as well? If so where can i find its ID?

Thanks,
Hoon