I know of 3 different ways to get the chief bwork ammy.
1: u can obviously buy the ammy from the sellrooms. 2. u can kill a bworker and get the bworker's token. 3. u can also just buy the bworker's token and try your luck.
If you decide to do option 2/3, you have a 50% to get a piece of the bwork chief set or the used bwork protection.
So, the chances of u getting the ammy with 1 bworker's token is pretty low.
oh to exchange the token for either the bwork chief set or used bwork protection is at -11, -41
http://www.wikia.com/dofus/Bworker%27s_token link on wiki where i found the coords and the information that i put here...
(3 different ways are just what i would probably do if i wanted to grab the ammy)