Looks like Brian hasn't released it to the general public yet for downloading but in response to somebody else asking about it.....
Originally Posted by Brian
1). I do have an import script for Gallery, I just haven't posted it yet because it's only been tested on one site. If you'd like to submit a support ticket via the Memebrs' Area here once you purchase the script I will be glad to import your current Gallery data for you.
So, yes, there is an importer but because it hasn't been widely used yet Brian may
want to be involved with the importing to make sure it's working.