Alrighty folks this is what you do..
First off find out where the vendor spawns and go there if he/she is there buy the item you want from them then go to war with them kill them and they respawn instantly so just ally them again and buy it rinse and repeat.It does take rep away from the faction so I wouldnt do it to many times strait but I hope that helps someone...
Well it only works with booty bay and those places but you dont really see many Limited Supply Items on anything other than them because goblins are very ugly and unloved so all they have is money :-('' sad isnt it?