There is a vendor behind a cage where the firing range is located. At first, the wares will be limited but when/if you become a paladin, the whole store is opened up. When you go down into the bunker, when you see the two turrets make a right instead of going straight around them. You can also sneak past the vendor into the warehouse and steal some fully repaired armor (and get neg karma)
If you do the quests you are given by the Elder, you will find several (5 or 6) dead BoS members with armor and weapons you can loot. The scouts, on the other hand are still living and only give you holodiscs.