At the links below, you will find Greek texts and resources that should work well with the translation tables on this site.
Koine Greek
Online texts
The Academic Bible Online site contains the text of the NA28 Greek New Testament.
Septuagint Online: Greek text of the Septuagint translation of the Hebrew Bible
Greek Bible Online: The text of the Greek New Testament
Bible Software
These apps contain modules with biblical and extra-biblical texts in Greek. They must be purchased and, while many of the modules contain unicode text, the apps themselves present significant accessibility blockers and issues. Use with caution.
Koine Greek Language Resources
The Bartimaeus Alliance of the Blind is a Christian organization that provides a library of braille books transcribed into .brf format, including several on Greek grammar and vocabulary.
Classical Greek Texts
The Perseus Digital Library: Hundreds of digitized primary texts in Greek, Latin, and English translation
The First 1k Greek Project is a repository containing many more Greek texts.
Classical Greek Language Resources
Thesaurus Linguae Graecae (TLG): A digital library of Greek literature