Are we talking some flavor of "futanari" which is basically "chicks with dicks" in the crassist sense. (Although they typically have the other female equipment too)
Or are we talking "she-males" which is a male to female "partially transitioned" person which often translates into effeminate looking men with Boobs + Penis?
Could try going for the "trap" stuff but that's usually a ("straight") male being unwittingly seduced/dominated by a she-male, rather than she-males pursuing other women.
To my understanding there isn't "much of a niche" for she-male on female stories. Usually the author will go for either a full transition, or the futanari route in such cases. But as I don't actively seek the stuff, I'm not going to say it doesn't exist, particularly given the wonders of the internet.
...that and the existence of fictionmania.tv among others. The stuff probably does exist out there, you're just going to need to dig to find it, and there may not be much that is widely available for that specific kink.