Seem to remember getting mine years ago from the tailor at STM, it was arranged through a crew mate who later transferred to the Kiwi AF, not sure if he was directly linked to the tailors though.
Only problem with said personalized hat is that it still says Sgt Y_G, Raf XXXloss. Never mind, had my moneys worth, and it is much more comfortable that the beret/SD option.
Y_G