You can find it at https://files.scene.org/search/?q=unreal
The file you want is /demos/groups/future_crew/demos/unreal11.zip - the latest version.
There are many other fantastic demos worth checking out, available there as well! It is an official archive. If you like Unreal, then you'll love its sequel, Second Reality!
You can also find recordings of ...
(Warning, all from Memory without checking any manual)
AFAI read the question, you're using an Apple II with highres graphics from BASIC and did run into memory problems - usually by interference of BASIC memory management with the graphics location. You 'solved' it (well, not rally) by moving to page two, but now you can't write any text.
Problem #1 Text ...