The datasets used here are samples extracted from the Amazon Customer Reviews data.
It is assumed that star_ratings of 1 & 2 imply negative reviews, whereas those greater than 3 are positive.
To fetch more data, download the files from https://s3.amazonaws.com/amazon-reviews-pds/tsv/index.txt.
You can then run the handy Python script:
python add-sample-datasets.pyto process them.