I am looking for Rambam's Hilchos HaYerushalmi (ed. Lieberman) (or a some other edition if it exists). Is it available for free online?
Dr. Aviad Yehiel Hollander, secretary of the Jewish Law Association, has posted a recent article from R. Zvi Stampfer on his groundbreaking work on Rambam's commentary on masekhet Ketubot from the Talmud Yerushalmi. This includes manuscripts recently identified from the Fustat geniza that were not available to Prof. Lieberman when he published his work on Hilkhot HaYerushalmi. In addition to Rambam's commentary, R. Stampfer's article provides an extensive discussion on the history and findings of the manuscript (all in Hebrew).
Just to touch on something Maimonist mentioned, there isn't anything illegal about this copy AFAIK. The essay appears on the Yeshivat Birkat Moshe site (the book was a jubilee published by them in honor of R. Rabinovitz, RY of YBM), and Dr. Hollander has regularly publicized R. Stampfer's work at his request. But that said, you could always buy the book (MiBirkat Moshe, 2011)
It's not available that I know of (other than possible illegal copies). However, it is available in both print and electronic forms from JTS/Schoken Books.
Hope that this helps. Kol tuv.