As far as I know, the only new movie themes are available either with version 7 or with a Plus membership to Photoshop.com.
In PE4, you have:
Entertainment: Performance Star
General: Comic Book
Happy Birthday: Birthday Party
Memories: Family Memories & Memory Box
Movie Genre: News Reel
New Baby: Watercolor
Slideshows: Pan and Zoom & Wedding Doves
Travel: Road Trip
Wedding: Outdoor Wedding
I have not seen any additional Themes for PE4. I was going to suggest looking on Muvipix, but as Steve did not mention that as a resource, I would assume that there are none there.