The best place to start is An Introduction to Algebraic Effects and Handlers.
All literature on algebraic effects, handlers, and other approaches to computational effects can be found on the frequently updated effects bibliography. Pretty much anything authored by Andrej Bauer or Matija Pretnar is relevant to Eff.
As warned on the first page, Eff is a prototype language, so most likely the syntax changed since the paper was published. However, we try to keep interesting examples up to date, so check out the examples directory and you will most likely find one corresponding to what you are looking at in the paper.
Versions from 3.0 onwards can be found on the GitHub repository. Version 2.0 was similar to version 3.0, except that it had a Python-like syntax. To our best recollection, version 1.0 resembled levy from the The Programming Languages Zoo.
The best place would be to open an issue on GitHub. If you want to do it privately, you can write an email to Matija Pretnar.