What are all the ways to increase the chance of a critical hit with kicks?

Question

This assumes that the user is a Brawler, Monk or has the Improved Unarmed Strike Feat.

• Cestus are gauntlets which deals 1d4 damage and has Critical Treat Range of 19-20×2.
• Improved Unarmed Strike pretty much say you can use your whole body as weapon and considered armed. Medium sized PCs deal 1d3 damage with Critical Threat of ×2.
• Now in regards to using Cestus, I assume the its Critical Threat of 19×2 on occurs with Punches or other attacks the require Fist and or Forearm.

Now besides taking the Improved Critical Feat, are there other ways to increase the Critical Threat range of your whole body with your Unarmed Strikes? Maybe Plate Greaves for Kicks, Spiked Elbow/Knee Pads, or even an entire set of Spiked Armor? Would an Amulet of Might Fist with Keen as an or one of the Enhancement Bonus(es) work?

Answer 1

Using a cestus would not be equivalent to an unarmed attack with a punch: it would be a cestus attack. Even if you had something such as feet-cesti it would only be a different attack and would not be considered a kick.

Improved Critical(unarmed strike) would work.

An Amulet of Mighty Fists with the keen special ability would work for piercing or slashing attacks. By default the unarmed strike is bludgeoning so you will have to find a way to change the damage type of your unarmed strikes. Hopefully some style feats do the trick (citation from paizo forums):

Hamatulatsu allows unarmed strikes to do piercing damage.

Boar Style allows unarmed strikes to do slashing damage.

Boar Ferocity allows unarmed strikes to do piercing damage.

Tiger Style allows unarmed strikes to do slashing damage.

Snake Style allows unarmed strikes to do piercing damage.

All the other ways of increasing your critical range will be either feats or spells that emulate Improved Critical in some way (and thus don't stack with it), mythic abilities, or 3rd party feats (like Focused Attack which makes you able to forgo all your attacks but one and increase your critical range by the number of attacks you forwent)