On eBay. Seller says total LBAs written are around 1.2M, which is like 1GB so these are basically brand new. Seems like a great deal for a great SSD cache drive.
Intel DC S3700 Series 400GB 2.5" SSD SSDSC2BA400G3 6Gb/s solid state drive | eBay
Intel DC S3700 Series 400GB 2.5" SSD SSDSC2BA400G3 6Gb/s solid state drive | eBay