The Lesson Tutor web site has American Sign Language (ASL) and Signed English (SE) symbols that are "reproducible for educational, non-commercial use."
These pictures are gif files that can be uploaded to TapToTalk Designer. When doing so, be sure to honor the Lesson Tutor copyright and use terms.
To upload one, first save it on your computer by right-clicking and using the menu that pops up. Then upload to TapToTalk Designer as you would any other picture file.
To access these symbols here are two Lesson Tutor links: Learn American Sign Language (ASL) and Signed English (SE) and American Sign Language (ASL) and Signed English (SE) Available Vocabulary Index.