This provides an OpenSCAD model for 6, 8, 10, 12, 14, and 20-sided dice. The design allows you to specify whether the numbering starts and 0 or 1, and whether the faces are counted by units or tens. For your convenience, I have uploaded STL files for the 6 dice types. By default, each die has a width of approximately 30 mm.

A recent design of mine was developed with Autodesk Fusion, but this one should allow for a lot more flexibility.

If you're familiar with programming in OpenSCAD, the code should be easily adaptable for other dice geometries, provided you define the points and faces as you would in a proper call to polyhedron().

The rendering was generated in Blender.

Enjoy!