Are you in the US or the UK? Device selection does vary by region.
In the US, Inovelli does have a plug in zwave pocket socket with two separately controllable smart socket. I don’t know if they’re intending to make a version as an in wall receptacle, though. @Eric_Inovelli May be able to say more.
https://products.z-wavealliance.org/products/2385
https://www.amazon.com/Individually-Appliance-SmartThings-Compatible-Inovelli/dp/B01K6J1Y1I
GE has a similar zwave module, 28177
https://www.amazon.com/GE-Appliance-Independently-Controlled-28177/dp/B0736311QF
Most of the Z wave in wall micros cannot handle the load required by code for US in wall outlet. They are intended only to control lighting, typically with a maximum of 10 A where US code requires plug-in outlets they have up to 15 A at least.
There is a zigbee in wall micro from SmartenIT , the ZBLC15 , but unfortunately Smartthings does not officially support the zigbee commands required to make dual independent control work.
https://www.smarthome.com/smartenit-4033a-zigbee-ha-wireless-dual-relay-on-off-load-controller.html
All three of these would require custom code, they don’t work out of the box with SmartThings because of the multi channel aspect.
I personally use the ConnectSense plug-in, which I really like, but it works with HomeKit, not smartthings.
2019 update
IDevices has released an inwall outlet where each socket is independently addressed. It doesn’t work directly with SmartThings, but you can get integration through IFTTT. (It also works with HomeKit.) but it’s expensive.
I do expect to see some zwave outlets with this option once the series 7 devices start hitting the market, but that might not be until mid 2020.