boostmobile.com, major retailers like BestBuy and at Boost dealers. The original Prevail, which is still available, was Boost's first CDMA Android phone and was notable for being Samsung's best selling Android phone in the US.
Unlike the first Prevail which is about as low end as an Android device can be, the Prevail II is a bit more up-market, but still moderately priced ($179.99 at launch.) Although the Prevail II doesn't support 4G LTE, it runs Android Jelly Bean 4.1 and should be a capable performer with specs like a 4 inch 480x800px screen, 1.4 Mhz single core processor, 1 GB RAM, 2 GB of available internal memory, 5 MP main camera and 1.3 MP front facing camera.
If the Prevail II looks familiar, it's actually the same phone as the Virgin Mobile Samsung Galaxy Ring which was released last month.