Has it been shown anywhere that Dr. Noonian Soong had in mind any plans for creating an android mate for Data? Or when he created him as a "fully functional" android, he had in mind that he would be able on his own to find a mate? Which for me is difficult to understand given that he did not have the emotion chip at the time of his creation.
There were no plans mentioned on-screen for Data to have an android mate. Data was likely made "fully-functional" to allow him to mate, or at least be intimate, with biological humanoids, not to mate with other androids, which would be rather pointless. It was Soong's wish that Data become as human-like as possible, so naturally he'd want to give Data all of the necessary...tools.
I don't believe this would have happened.
Along with Brian's answer, it is worth bearing in mind that Data viewed Soong as his father and Lore and B4 as his brothers. Therefore it's reasonable to assume that if Soong had created a female android, Data would consider her to be his sister and thus not an appropriate mate.
I'd expect Dr Soong to be very wary of the 'Frankenstein's Bride' problem so it seems very unlikely that he would have planned to create a partner for Data.