STEP 1
Find the vendor that sells what you wanna buy - look at Website to see who sell
Then buy the first stock of the item you want to buy.
STEP 2
Go into your Reputation tab and select "At War" with the vendor faction.
Then simply kill the vendor!
You will find that these sorts of vendors respawn very fast - sometimes IMMEDIATELY!
STEP 3
Return to your Reputation tab and de-select "At War" with the vendor faction.
Open the vendor up and you will find the "LIMITED STOCK" item, RESTOCKED!
STEP 4
Buy stock and repeat
You will loose a little Rep doing this (10-25 pr kill)