Some are available if you are a Plus member of Photoshop.com.
Otherwise, you can use any transparent SWF files -- though I don't know of a source for them.
If you are on a Windows machine, there are tons of ClipArt available from MicroSoft, for MS Office. They also have some Video and Still Images, as well. They are free to download, and MS even offers a cataloging (and download enhancing) application for those.
You might also find some useful stock video footage at Muvipix.com, that is available for purchase, or free download, to subscribers.
ProDAD's Vitascene also has some Effects, similar to some that you describe, so might be worth looking into.