What version of Premiere Elements, what computer operating system?
Video and audio transitions available from Adobe are what are found within the project.
You could check 3rd party sources online, free and non free. Many transitions are listed for Premiere Pro, no mention of Premiere Elements.
I do not know of a list of these 3rd party Premiere Pro transitions that are known to work with Premiere Elements.
Many of the transitions within the program are from NewBlue. You could start by checking out its web site to view its offerings and note its requirements for use for a given transition. There are probably other transition vendors who can be found via Google Search. I have not used them since there are numerous transitions to select from the Adobe offerings. Have you explored them all? And, you can edit them.
Please consider. Any questions, please do not hesitate to ask.