Despite the fact that old and bold Navs are eligible to continue wearing the Nav Brevet, you won't have a lot of luck from stores.
I qualified as a Loadmaster a , ahem, few years ago but as soon as this WSOp crap started, the LM brevets dissappeared and if I want a brevet for my No1's (which come with one of the naff WSOp brevets as default), then I end up apying six quid for it.
Beancounters, your end is nigh!
Rant Over
WM Out