This is not available for mainstream Windows 10 users yet.
In the Latest Windows 10 Insider Preview of Windows 10 build 18267, Microsoft have updated the Touchscreen keyboard in Windows 10 to make it easy to access, commonly used symbols such as currency symbols, mathematical symbols, arrow like symbols and Greek letters.
I left Windows feedback for Microsoft to make a modern character map last week based on their emoji panel. It may be coincidence but it seems like they took this feedback and instead applied it to the touchscreen keyboard:
The touchscreen keyboard can still be accessed on non-touch systems by right clicking an empty area on the taskbar and selecting show touch keyboard:
Once this is done you will see the touchscreen keyboard icon beside the system clock. You can open it by left clicking with the mouse:
In the Windows 10 Insider Preview build, press &123 to access the numbers and symbols:
Press the Ω key to access the new symbols:
Some screenshots of the new layout (the video above shows more details):