I've read the 5 books of "A Song of Ice and Fire", and what I've walked away with is, the Dragon eggs that were given to Daenerys during her Wedding reception were not the only ones left in the world.
Daenerys receives 3 Dragon Eggs from Illyrio Mopatis. I know Illyrio does not manufacture dragon eggs. I suspect he must've purchased those eggs from someone who is from Asshai or someone who knew someone from Asshai.
Also, if someone sold 3 dragon eggs to Illyrio what's to say that this person does not have a factory full of those dragon eggs.
Next, Euron explained that during his voyage from the forbidden sea that he had a dragon egg and that for some specific reason(I forget) the dragon egg happened to fall into the middle of the sea.
Based on these findings, I believe that there are a lot more dragon eggs laying around.
But, I think they are harmless because as we discovered that the only way those eggs will hatch is if it lays in fire.
If there is anyone who is familiar with the dragon egg theory, please feel free to chime in.