Hello,
Ever since the hotfix in July to add the Brutosaur to the black market loot crates, no Brutosaurs have shown up as a regular listing. Prior to this hotfix, Brutosaurs were spotted every ~10 or so days, and in the past 6 months there have been zero. There was a blue post response that this behavior is not what is supposed to be happening:
TSM data on the lack of listings: https://www.reddit.com/r/woweconomy/comments/qxll21/tsm_has_no_evidence_of_the_bruto_mount_being/