Here is a player species designed by one of my players, which I have statted up: the Gearwork Android. Designed to use only kinetic energy, it allows you to explore sentience in a kind of android different from the Soong-type.
How can you integrate this species into your campaign? Under the backstory created, there are twelve units in total, and they have been deemed sentient for about six years. I left the creator species unspecified, so you can choose whichever species that fits your campaign. The player hopes to create a Gearwork Android supporting crew member aboard their starship in 2371, but since it’s been established that Soong-type androids are the only sentient androids recognized in the Federation, likely the Gearwork Androids originate outside of the Federation (or their planet had just joined the Federation). We haven’t introduced the character yet, but a likely introduction would be as an observer aboard their ship, or as part of an Officer Exchange Program.
Here are some possibilities for the creator species in the Alpha and Beta Quadrants, each of which would put a unique spin on the nature of the Gearwork Android in your campaign: the Zibalians; the Talarians; the Tzenkethi; the Breen; the Sheliak; the Caldonians. Or, the aliens from the Biological Clock adventure in These Are The Voyages Vol. 1. Or, ignore ‘The Next Generation Era only’ tag and introduce them in earlier eras.
I borrowed the image of the clockwork repair droids from Doctor Who, but feel free to conceive the look of the Gearwork Androids as you wish.