How can i get dataset from facebook for sentiment analysis?

or you can look into this global ML dataset repository: https://archive.ics.uci.edu/ml

You can use aforementioned datasets or if you want to scrap the data yourself there is Facebook graph API.

PYLON provides access to previously unavailable Facebook topic data and has some price.

If you don't exclusively want Facebook datasets you can easily get data from other sources like (twitter, google, Wikipedia) using pattern.

I could not contribute anything beyond the previous excellent suggestions concerning relevant data-sets. However, this article might provide useful heads-up about what to consider and plan ahead for concerning transparency and reproducibility:Crosas, M., et al., 2015. Automating open science for big data. The Annals of the American Academy of Political and Social Science, 659 (1), 260-273

You can also check out Nvivo tool which extracts the facebook data using plugin called ncapture and also auto coding feature can be performed to get sentiment analysis and polarity detection.

Here is the dataset with movie reviews.

This is a large dataset, with classified data as positive and negative, which makes your task to train easier