All Movie Themes are downloaded from within Premiere Elements 11.
Have you been there and done that?
See Instant Movie tab at bottom of Expert view and all the theme choices with the blue ban at the top right of each. You need to click on that blue ban to initiate either download for that one or download all. It can be a long process depending on your Internet connection and the Adobe Server.
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As far as I know that is it.
In the days of photoshop.com and versions earlier than 11, if you were a photoshop.com plus member you might get extra items once in a while (not sure if that included movie themes).
If you know the following already, please disregard. You can customize the Adobe selection of Instant Movies. Once the Instant Movie is completed you can use the command to break it apart so that you can add, subtract, and move things around. I suspect that is your best opportunity. I have not seen any online.
IIRC, Robert Johnson (used to frequently post here, and is still active on Muvipix) WAS working on some Themes/Instant Movie Presets, and planned on posting those on Muvipix.com. When I looked there, I did not see any PrE Movie Themes in the Resources area, but perhaps they are elsewhere and I just missed them, or perhaps Robert gave up on that project? Still, might be worth a bit of time spent on Muvipix.com, in case I just overlooked those.
Good luck to the OP,
I checked muvipix before my previous reply to Harriet. I found nothing there relating to free or for sale extra movie themes.
I did find the following Robert Johnson older thread (2007) on the matter of Editing Existing Movie Themes. From what Harriet wrote, I did not believe she had any interest in that approach.
Ah, I feel better about my failed search now. Worried that it was because I failed Boolean 101... ?
I would assume that Robert gave up on his project - maybe too much work, with too little interest.