Try nemirc's store at Renderotica, he has a pose set that includes one.  Also RuntimeDNA has a set for V3 Male called "Adrian" which includes a poseable penis figure. You might need to do some morphing or repositioning with it, as it's intended to fit the V3 male's hip shape, but I wouldn't have thought that would be too hard (no pun intended, hehe)

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"you are terrifying
and strange and beautiful
something not everyone knows how to love." - Warsan Shire