There seems to be hardly any SLC SSDs left, particularly on the client side. On the enterprise side, even they seem to be replaced now by the MLC based drives.
The only one I could find was the Fujitsu FSXtreme 240GB SLC SSD, which costs about twice as much capacity as a similar 256GB MX100. It's slower though than the 850 Pro.
I suspect there simply isn't a large enough market of consumers willing to pay the SLC premium?