How do I get cards from Modern Horizons into spell shop?

[w16807]

Hello, just wanted to say thanks for continuing to support Forge as I really like testing out new decks with it. Forgive me if this is a redundant question, but I seem to be unable to get cards from MH and MH2 to appear in my spell shop. I try traveling to other worlds and then returning, and setting the shop to stock a huge number of cards, but I still never see cards from these sets show up. I see other recent sets like VOW and Strixhaven. Is there something I need to do first? Or maybe is there a way to acquire cards from those sets without buying them?

I'm pretty sure I've already unlocked them as I see some cards from them in my inventory and I can also select them in booster draft mode.

An unrelated question - is there a way to update the opponents in quest mode with more recent modern decks? Any links would be greatly appreciated.