Via the API you would have to fetch the client and then fetch his services, and manually sort out whether they have an active SolusVM service and what the main IP may be.
If you simply need a list to reference, a CSV report may be useful. Create a custom report under [billing] -> [Reports] with a query for what you want to fetch, e.g.
SELECT REPLACE(`clients`.`id_format`, '{num}', `clients`.`id_value`) AS `id_code`, `service_fields`.`value` AS `main_ip`
FROM `clients`
INNER JOIN `services` ON `services`.`client_id` = `clients`.`id`
INNER JOIN `service_fields` ON `service_fields`.`service_id` = `services`.`id`
WHERE `services`.`status` = 'active' AND `service_fields`.`key` = 'solusvm_main_ip_address'
GROUP BY `services`.`id`, `clients`.`id`
ORDER BY `id_code` ASC;