After conducting a thorough investigation, it's clear that there is no official 23rd episode of Boku no Pico. The series consists solely of the original three OVAs, and no reputable sources have confirmed the existence of additional episodes.
(released October 9, 2008): Introduces a third character, Coco. Clarification on "23 New" boku no pico ova 1 2 3 23 new