What computer operating system are you using for your Premiere Elements 13/13.1?
Two possibilities for the not finding Chroma Key or Green Screen Key
1. You are working from a Mac computer - Premiere Elements Mac does not have Chroma Key or Green Screen Key (Windows Only, both of them).
If this applies to you, use Difference Matte (Expert workspace/fx Effects Tab/Keying) or, as some would suggest, Videomerge (Expert workspace/fx Effects Tab/Videomerge). I prefer Difference Matte.
2. You are working in the Quick rather than the Expert workspace of Premiere Elements 13/13.1. The Quick workspace does not have all the options that the Expert workspace has.
Please consider the above to see which applies to your situation. If any questions or need clarification on this matter, please do not hesitate to ask.