Way to get old podcasts in iTunes
As far as I remember you can add them "manually" by clicking on the list. Just search for the show on the iTunes and click on the individual shows you want to download.
Edit: it seems that the iTunes store just shows episodes of the certain period.
From Apple's Support - Podcasting Frequently Asked Questions (FAQ):
Troubleshooting podcasts
I subscribed to a podcast, but I don't see all the episodes—only the latest. How come? iTunes will only display the podcast episodes that are included in the podcast feed. Many podcasts have the older episodes archived on the web. Check the podcast hosting site to see if older episodes are available.
In iTunes, you can only download the shows that are in the show's RSS feed. For any shows beyond what's on the feed, you will have 2 options.
- Go to the website and download each one individually.
- Email the host and see if they can send you a Zip file with all previous shows.
sometimes, you might delete the undownloaded podcasts from your list. to get them back, so you can decide to download them, collapse the podcast branch, then shift-click the arrow to expand it again.