Computer scientists use A-F as number glyph extensions and a hexadecimal system that fits the memory organization of common computers - a 2-digit number fits exactly into one memory cell (one byte, 8 bits, the smallest directly addressable memory unit).
Still, while thios worked for the computer sciencetist, I think there is little hope to establish a 12 based system for everyday use, even if it'd have benefits, since the 12 includes so many small numbers. 2,3,4 and 6 are all evenly contained in 12. The next better base is 30, which has 2,3,4,5 and 6, all of the first 6 numbers (I didn't count the 1, because it's not useful). But 30 number glyphs are difficult to remember, so the 12 is likely more practical for this reason, even if it lacks the 5.
While doing my research on the question of the 10 vs 12, I also found this:
http://www.dozenal.org/
There is a real organization trying to promote the 12 based systems. I had not heard of this before. A pity, but I think it's good that there is an organization trying to promote the 12 based system and explain it's benefits.
I have not yet found out though which glyphs they suggest for the 10 and 11.
But I found another 12 based system: Musik - in western music an octave (the interval of a base frequency to double the base frequency) is split into 12 notes.