Magical realms or no, there are a lot of ways to traverse realms. I remember when Emma became Dark One and the Apprentice gave Regina a wand she had trouble using. But hey, she could have used a fairy crystal....or
1. Magic Bean
2. (Dark) Fairy Crystal
3. The Sorcerer's Wand
4. A sprinkle of Pixie Dust
5. A Shadow ripped by Shadow Tree Sap
6. A mermaid
7. Two mid-tier witches at a magical nexus
8. One high tier witch.
9. A deity
10. A genie wish
11. A wishing star
12a. The Dark Curse (oh yeah)
12b. A voicemail spell with heart dust (aka whatever Hook called a Dark Curse)
13. (Energized) Kraken's blood
14. Random Tornado events
15. A rabbit with hole-digging skills
16. Looking Glass (although that's specifically to Wonderland)
17. Author's pen
18. Silver Slippers
Bonus: The Writer's Room
I seriosuly hope they don't add more. It make sense between magical realms (even though there are portals within the same realm) and common place, but reuse the same stuff rather than making more....sigh