The only way to obtain these cards is now through 3rd party marketplaces like Ebay
These do the dual purpose of both playing into the journey of our protagonist too, and acting as spells that our commander will be able to cast during combat
Delver of Secrets is a notoriously fickle card to try and accommodate in cube, while most of the other suggestions require too much setup for too little payoff
2: Castle of Aaargh (Dark Depths) The Black Beast of Aaargh (Marit Lage) Sir Bediveres Scales (Ashnods Altar) The Bridge of Death (Door to Nothingness) To get notified as a reminder of when these sets go on sale, you can head to the official Secret Lair page here and pop in your email.
Illustrated by Alexander Mokhov Standard Not Legal Alchemy Not Legal Pioneer Not Legal Historic Legal Modern Legal Brawl Legal Legacy Legal Comp
Teferi, Master of Time I typically avoid planeswalker ults on lists like this because achieving them is incredibly inconsistent, but Teferi, Master of Times static ability makes it much more reliable than most and all the card filtering helps sculpt the perfect hand for those two extra turns