vBulletin 3 and 4 are no longer available to new licenses.

The new licenses sold after January 1, 2020 will no longer download the versions of vBulletin 3 and vBulletin 4.
https://forum.vbulletin.com/forum/vbulletin-sales-and-feedback/vbulletin-pre-sales-questions/4433239-vbulletin-3-and-4-are-no-longer-available-to-new-licenses

See original post by invalid@example.com (Laniakea)