This ultra-traditional (not a technical term) sect of Catholicism is effectively its own denomination (link). They would claim, I believe, to be "Catholic" and they claim that the real pope is locked up in a Vatican dungeon, so they cannot really be called Sedavacantists.
The folks out there who have been trying to wield the "Sola Scriptura causes disunity" claim have trouble dealing with this kind of data. Rationally, though, if cultic groups of this sort can crop up without any reference to Sola Scriptura, why besides blatant exercise of the post hoc ergo propter hoc fallacy would one blame the large number of denominations on Sola Scriptura? To put it a different way, don't groups like this demonstrate that people tend to form their own groups regardless of Sola Scriptura?