I have recovered the installer using a offical download link from the old bigbrainz.com. I have the online launcher for the game but currently almost figured out how to get the full game! If you use the installer and go to the timezAttack and AddSub Folders and delete the files named iamfull.txt after you do that you get online launcher

Here is the download link this one is from me so it isn't offical https://www.mediafire.com/file/6dror6ze54ih0kc/Win_BigBrainzHomeInstallerFull-L2.0.3-TA6.73-AS2.16+(1).exe/file