As above, made by Pirate's Lair in the USA, with full installation instructions.
Bought as part of a package - I wanted the other bit!
Will throw in a "carbon look" fender extender marked K1200 >05 that I bought here; it does not fit Slant K12/13, so I presume it is for the Brick K12 (i.e. K12<05).
£20 posted.
Photos of backrest from original seller.
My photos of fender extender
Cheers,
A