Traditionally Halloween was the biggest night for pirate radio broadcasts. The bulk of the pirate radio broadcasters are just below the 40-meter amateur radio band: anywhere from 6,850 kHz to 6,970 kHz and typically on a frequency spaced at 5 kHz. The most popular frequency is arguably 6,925 kHz, but I often log pirates on 6,935 and 6,950 kHz.
Here’s a good reference list in case anyone wants to do some searching
https://www.hfunderground.com/wiki/List_of_Pirate_Radio_Frequencies