We’ve released the new service for getting client information — the Clients service for API version 5.
You can use the get method. An advertiser's representative can get the advertiser's parameters and personal settings. An agency's representative can get parameters for their client advertiser and the user settings for the username specified in the HTTP Client-Login header.
You can find more details about clients and roles of Yandex.Direct users in the documentation. See output client parameters in the method's documentation.