Download demo game resources from
https://archive.org/download/tucows_286139_Quake_III_Arena/linuxq3ademo-1.11-6.x86.gz.zip/linuxq3ademo-1.11-6.x86.gz.sh
and select the downloaded file below.
You need to paste the link into your normal browser. Clicking the link here might not work.
Alternatively, if you have already purchased Quake III Arena, you can upload full game files.