From mag.the4blades.com: You should be able to see ‘Subscriber Bonuses’ in the menu bar. You can find the bonuses here.
From your mobile device: They are within the app and marked with a ‘Private’ banner.
Please note: Subscriber bonuses are available to current subscribers only. Past subscribers retain access to all their paid issues, but no longer get access to the free bonuses, which are offered as a perk for being a current subscriber. If you are not currently subscribed but want to access the subscriber bonus issues (and who wouldn’t?), consider starting a free 30 day trial!