Law can be obtained as quest reward for doing Sherrifs request in sanctuary. Laws can also be collected from the Sherrif of Lynchwood. They still work with the Shield order. Depending level you are and luck of the drop they can actually be better versions of the Law quest reward.
To TC keep farming Sheriff of Lynchwood she drops it fairly consistently. I generally got one after 4-6 tries. Some will be Fine Laws and some Leather Laws. Make sure you search carefully because sometimes her loot can spill in weird spots depending where you killed her. Also this fight can be good for grinding XP depending on what you are getting. If you take your time before killing her the Marshalls will respawn for awhile before they run out.