John K. Pe-ta did futanari (
thread) but is not part of his regular content. I also mentioned his artwork got noticeably better in recent in times.
An author first has to do a series with supernatural content, if he/she does supernatural then the chances to find a given process are high. K. Pe-ta still didn't make a supernatural series from what I remember, it did a few with tentacles or ghosts but mostly as omakes or bangais.