We are sorry to know you have not been able to locate any Intel® SSD DC S3500 Series 340GB, M.2 for sale.
As noted in the specifications from http://ark.intel.com/products/84290/Intel-SSD-DC-S3500-Series-340GB-M_2-80mm-SATA-6Gbs-20nm-MLC# @specifications Ark.Intel.com for this drive, it was launched on Q4, 2014. It is normal for some products to go out of stock, furthermore, since this is a business class SSD, and M.2 is not a mainstream form factor yet. You should be able to locate some through specialized online stores, or you mayhttp://www.intel.com/buy/us/en/reseller look for a reseller in your area to check about this.
There are two different SSD ordering codes that you can use when searching for this SSD model. The packaging and accessories may be different, but the SSD will be the same:
SSDSCKHB340G4 - Intel® SSD DC S3500 Series (340GB, M.2 80mm SATA 6Gb/s, 20nm, MLC) Dual Sided, Generic 100 Pack
SSDSCKHB340G401 - Intel® SSD DC S3500 Series (340GB, M.2 80mm SATA 6Gb/s, 20nm, MLC) Dual Sided, Generic Single Pack
The drive should be in production, however, we will research further on this since we checked and it appears to be out of stock in major stores.
We advise you to locate an Authorized reseller using the link provided before, as they may be able to get the drives for you even if they don't have any in stock at the moment.
Could you let us know how will you be using the drive; for personal use, business, government, or other?