So I'm on my way to kill the Four Kings and in order to do so, I need Transient Curses since I don't have any magic.

I went to the merchant and she does not have any of them...

I did buy Transient Curses from her before so I have no idea where it went.

Do they run out of stocks?

Because if they do... I'm kinda screwed...

It is this a bug or what is it?

They run out of stock, I'm pretty sure.

You could always hit up the depths and get cursed so that you can kill the ghosts and farm some more transient curses (they drop them), use the Covetus Gold Serpant Ring to increase drops.

Don't know what to tell you. look around New Londo for some dead bodies, they usually have transient curses on them.

@Sign said:

You could always hit up the depths and get cursed so that you can kill the ghosts and farm some more transient curses (they drop them), use the Covetus Gold Serpant Ring to increase drops.

I suggest this as well. They sometimes drop the Jagged Ghost Blade as well. That allows you to hit them.

The drop rate on Transient Curses with the serpent ring is ridiculous. I got 20 while using just 1.
 
It's also possible to just run past the ghosts. They are slow. Assuming you've lowered the water already, if you enter New Londo Ruins from Valley of the Drakes (shortcut in Darkroot Basin) there's only a couple that are easy to avoid between the entrance and the boss door.

Do you have a ghost blade you can hit them with?

Oh God... I was not expecting this at all....

It's not @nohthink said:

Oh God... I was not expecting this at all....

It's not that serious really, just get cursed and run through that relatively short area to unlock the floodgate then after that you can get uncursed for a slight fee and just make quick runs for the fog gate without having to fight any of the ghosts.

Ghosts are the worst.

@jozzy said:

Do you have a ghost blade you can hit them with?

They will still phase right through your shield and the ghost blade is very short range

making it highly impractical.

I think the ghosts also become more aggressive when they know you can't block anything. Once you get a transient curse item/get cursed in the sewers and are back to fighting the ghosts, make sure to equip the Gold Covetous Serpent Ring from Sen's Fortress. You'll have a nice stash of them built up in no time.