There's a supplement called l-lysine that's supposed to supress the virus that causes cold sores. However, the last time I had one, I had a dentist appt and they prescribed Zorivax and it was fabulous--I got the cold sore that day and so it was pretty big by the time I got the medicine, but it totally stopped it. I think there's a generic available now, but don't recall the name.
I doubt it's natural, but I work with the public and trying to smile with those things without making them crack & bleed is impossible, plus, people look at you like it's leprosy! I've gotten them for years--my first time, I had 12 at one time--they all grew into one big one! I was 15 years old! What a trauma! At that time, Campho-Phenique was the only thing and I'm not sure it was good for anything besides some temporary relief.
Good luck getting rid of yours.