Question

How to get elemental boron from boric acid

Answer 1

It'd be possible by adding conc. aq. borax to excess conc. aq. HCl, the boric acid should precipitate, and then reducing the boric acid with charcoal.
This will produce the amorphous allotrope; it can also form a VERY hard crystaline form by recrystalisation from molten aluminium (which could also be used for the reduction).
Boron makes a damn good fuel once you get it lit, too.