Buying bowstrings, wraps and whatnot.

Where is the merchant for this kind of junk? I want to upgrade the stuff I got with the Bonus Mission Pack, but I can't seem to find a vendor for any of this stuff anywhere, not even in Kamadan or Lions Arch. I know it exists because I can unlock various junk for a PvP character, but that doesn't actually give me the item, just unlocks it for a PvP based character, which I am not, so I'm wondering where the PvE based version of that guy is.

You have to either salvage thme from loot drops or buy from other palyers. No merchants for these things.

There is no merchant for weapon upgrades, unfortunately. Like Premium said, you have to salvage them from weapons you find or buy them from other players.

You may want to take a look in our trading section of the forums to see if you can find what you are looking for there.