Uh oh.
The upgrade pack has been located! They are definitely Knights of the Blazing Sun and called " ... Command Pack". There are 3 heads on one sprue, a commanders head with body and 3 feathers on helm, a head with a bugle, and arm with a standard with Blazing Sun motif, an arm with a huge sword, and 5 shields with Blazing Suns motifs on them. Price tag reads $16.50.
Uh oh, sorry, these bits are definitely going to be used by me on a set of knights at some point.