sort of, people have programs to dump them somehow. i don't know how though.
If you use your flashcart, you can download the demos directly to there. Some "captured" demos can be found somewhere, but they are pretty old. A google search may find some.
As for new ones, I don't know if people are still trying to capture them or w/e
But yeah, there really should be a homebrew program searches for demo's then puts the demo onto your sd card.
Bookmarks