Where can I find unit award orders that authorize me to wear them?

Most units have some sort of display that showcases the unit awards. You are authorized to wear the award(s) while a member of the unit. If you were a member of the unit during the actual award, then the award becomes part of your permanent authorization and you would have received the orders at the time of award. Your S1 should be able to assist more

S-1 should have it, if there are no older S-1 members, check HRC, and if you run into problems there ask your Unit Historian, if you don't have one check your Lineage and Honors.

That's my 2-cents.