Hey Rookie,
I'm also applying for Phil MA this cycle, and I've found a few resources:
https://www.uvm.edu/wid/writingcenter/tutortips/philosophy.html (General advice on the writing sample, includes a few examples of successful undergrad papers)
https://era.ed.ac.uk/handle/1842/1746 (Some graduate theses in philosophy)
Neither of these are successful writing samples per se, but they're in the ballpark.
If anyone has a successful sample they'd be willing to share, I'm also interested.