Yeah I think I'll go for Weapons too since I'm on hard, wanna try a horde I spotted. Is there a way to find the horde again?
If you don't remember then, no, you won't get a method to locate hordes for a long, long time. You will happen across plenty though.
However I'm guessing you saw the horde in the rail cars near the NERO checkpoint at the northern tunnel? It's probably the first one most players see.
You aren't locked out, it just takes longer to build trust.
However I would just press on to the third camp instead of trying to build up trust at Copeland's. The third camp is a lot quicker to build trust with and you can get a lot of significant bike upgrades there.
Another reason to build up trust quicker with Tucker is that it's the first camp where you can unlock (weapon spoiler)
the machine gun (AKA Horde Killer). I had to keep an LMG I found in the world as my secondary weapon for a huge chunk of the game until I unlocked Level 3 at Tucker's.