Frankly, freeloading off other folks' work makes it seem like you're just being cheap and lazy. You can take 360ºx180º panoramas with a smartphone and fisheye attachment if you know what you're doing, and using a plumbline to keep yourself at least close to rotating around a no-parallax point isn't that expensive. The defects aren't from your hardware/software combination, it's from your shooting technique and/or choice of scene (smaller spaces are tougher to shoot than larger ones). Not to mention that Hugin is open source.

That said, Flickr allows folks to attach rights, including Creative Commons, to each photo they upload. These rights can be anything from public domain to fully copyrighted. The nice part about Flickr, is that you can then limit a search by these rights. I would, however, recommend being VERY careful if you choose to use Creative Commons as your search, as the CC licensing scheme has several options that do NOT allow for derivative works, and many require proper attribution and non-commercial use. I'd recommend sticking to public domain images as much as possible.

Once you've limited your search to the appropriate licensing, you can then search on the equirectangular tag. Nearly all 360ºx180º images on Flickr use that tag, because that's one of the ways to cue the interactive viewer on Flickr.