All I can tell you is Migratr as a migration software from flickr to zooomr but I'm not sure it works for undisplayed pics in flickr. Ask the author.
http://www.callingshotgun.net/

Although I've never attempted this myself, one thing that might work would be to use Migratr to move over 200 photos, then (after verifying successful migration first) delete them from flickr. The next 200 would then show up. Rinse and repeat.

The only problem with using Migratr on an elapsed account, is that you won't be downloading the original photos, just the resized ones (usually around 1280x...).

If you want to preserve the originals, and access the rest of your photostream, then subscribe to Flickr for a year for $25, and use Migratr then.

It's always worth having at least 2 accounts for your photos on the web. It gives you flexibility to switch between them if need be, and they act as a backup for each other, incase you have problems with either site in the future.