Shawn Sijnstra has written an Infocom interpreter for the Model 4 that will allow you to play most v3, v4, v5, and v8 Infocom games. He writes:
New software release: M4ZVM – The new TRS-80 Model 4 player for v3, v4, v5 and v8* inform interactive fiction games (such as Infocom and others) is ready for download, play and feedback. It supports most features you would hope for including timed input, game saves, and transcript printing. 128k minimum. Full source code and binary available – if you do give it a go, let me know how you find it! Finally you can play adventure games like A Mind Forever Voyaging, Beyond Zork: The Coconut of Quendor, Border Zone: A Game of Intrigue, Bureaucracy, Nord and Bert Couldn’t Make Head or Tail of It, and Sherlock: The Riddle of the Crown Jewels (and many hundreds more) right on your model 4/D/P! Download your copy today!
Full list of credits, features and issues as well as the source and compiled code are in the Gitlab page: https://gitlab.com/sijnstra1/m4zvm
Once you download his executor, you can find the Infocom files all over the web such as on Abandonware.