Only 2 Missiles are needed to get Kraid to stand up, after which they are farmable. Getting up during Phase 2 can be done by jumping on Kraid's projectile platforms or a well timed crouch jump + down grab.

Requires:

{
  "ammo": {
    "type": "Missile",
    "count": 2
  }
}
{
  "or": [
    "HiJump",
    "canWalljump",
    "SpaceJump",
    "canSpringBallJumpMidAir",
    {
      "and": [
        "canDodgeWhileShooting",
        {
          "or": [
            "canCarefulJump",
            "h_canCrouchJumpDownGrab"
          ]
        }
      ]
    }
  ]
}

Clears obstacles: f_DefeatedKraid