Where can I get a display screen with 30 Hz or less refresh rate?
The information you're referring to is outdated. Flickering, banding, and other artifacts caused by refresh rate issues is primarily seen on CRT monitors -- LCDs are largely unaffected.

If you want to reproduce this issue intentionally for the purposes of an experiment, you will probably need to find an old CRT monitor. The effects created by a monitor of this type cannot be reproduced accurately on an LCD.