I can confirm that Brunhilde does sell the sallet when Bastok is in first (maybe not always, but she did today). It cost around 52k with max Bastok fame, so you're better off buying it from the AH for 8-9k.
While the defense is great for this type armor... it really isn't great for Dark Knights...I use this now but it doesn't give any Stats boosts.
if you got the money (Farm/BCNM) then go for the Valkyrie's Mask...which is expensive I know...going 300-350k on Unicorn server but you can use this untill lvl 60 Chaos Burgeonet.