Wit's End is more of an offensive "bruiser" item, not really a tank item.
Abyssal is the same as wit's end, only for people that don't necessarily auto attack that much, and it's also situational based on the number of magic damage dealers on your team (not worth getting if you're the ONLY one doing magic damage).
Merc Treads are more for the Tenacity, the MR is just kind of a bonus.
Locket, let's be real, doesn't give NEARLY enough MR for a "tank" item. You get it to boost your teammates MR with the aura, and the shield.
Maw is an AD Caster version of Wit's End (without shredding their MR) with a nice shield, but it too... is hardly a "tank" item. It's also more efficient to keep the hexdrinker throughout the game, only upgrading to Maw as the 6th item.
GA is a situational 4th or 5th item, and doesn't do that much if you have no health.
QSS is amazing on certain champions, but unless you can make use of the AD, you're just going to sit on a QSS which is most likely used for the active only (if you remember to use it).
All that said, yea... there are only really 2 choices in MR if you're going to build tank, Trinity-Tank, or BotRK Tank.