How to get archive subscriptions

Hello,

I'm trying to write a simple script similar to add-apt-repository,
but that it's able to handle private PPAs also.

Exploring the API, I've been able to get the teams for a person
and the PPAs for each team. However, in the PPA (archive) object
I've not been able to get the subscriptions for a person.

It seems it's possible to create a new subscriptions through newSubscription
method, but I'd like to get subscriptions that are already in place
such as the ones obtained in:
https://edge.launchpad.net/~<login>/+archivesubscriptions

Is there any way to do that?

Best regards,
    Javier