I would just keep an eye on fantasy subreddits and perhaps sign up for publisher email newsletters or follow authors on Twitter. The two free that I got this year (The Whitefire Crossing by Courtney Schafer and The Winds of Khalakovo by Bradley Beaulieu) were both newer authors whose second books were coming out. SF and not fantasy, but David Weber's first Honor Harrington book, On Basilisk Station, is free.

And if you're feeling adventurous, here's the current list of the top 100 paid and free bestsellers in fantasy on Amazon. Most of them are probably bad, but there could be a few gems there.