Hey @npolyak ,
good question! I’d recommend two routes, although I’m sure there are more:

1. https://www.kaggle.com Has a large number of free to use datasets from competitions and publicly shared datasets. 
2. https://www.mockaroo.com Allows you to generate some mock data. I believe it’s limited to 1000 rows for the trial but I’ve found this useful in the past.

Hope these help!
TheOC