You can see above that I decided to do derm late...after I already matched into internal medicine. So I interviewed during that intern year. Three outside-the-match spots came open while I was an intern and I had two offered to me. I was called to interview for another spot that came open at another program that I wanted to attend but there were four applicants and the interview was a week away so I had to turn it down (I took a bird in hand, essentially). Of the two that offered me a spot, one was in Manhattan and they had a derm spot but the catch was the subsidized resident housing was full. So I took a spot at a good program down South.
So, derm spots often come open for the following year. I was in play for three of them: one because it was a program that secured funding for an additional resident at the last minute and two because they had incoming residents that decided not to show up for their PGY-2 derm positions. It happens. One of these very spots was turned down by one of my med school classmates. She was a great applicant but decided to marry an anesthesiology resident and be a housewife.
The catch is that MS-IVs can’t take them because they still have an internship year to complete. Since I was applying as an intern I got two offered two great spots that I never would have in the regular match. My two fellow derm residents were both valedictorians of their respective medical schools, while I was AOA and a good applicant I was outside the top 10% of my med school class. That’s because there was a much smaller applicant pool I was competing with (other interns and research folk).
So, how do you find them? Apply widely across the country and be available for the next calendar year (ie already in your internship or already completed one).