How can I get iTunes on my new MacBook to acknowledge an existing Podcasts directory?
This can happen with any file type, not just Podcasts, and I've suffered from this a few times when I move my iTunes library about, especially with TV Shows.

The only solution I found was to move the episodes out of the iTunes Media folder, then use the Add to Library in iTunes to add them back in. This forces them to be added to the .itl even if there's already a malformed entry for that file.