'Looking for something that is selling well'
As you have correctly identified peter, everyone else is doing the same and that is what makes it so hard finding drop shipping resources for popular products, the market is always completely saturated.
If drop shipping is going to be your platform, I can only suggest you go in the opposite direction, look for markets that aren't popular on the surface because they are not being supplied.
Niche is the term used, and when people discover products that fit these types of markets they see that they can generate solid sales without selling all of the 'popular' items.
Now your next question will most likely be, how do I find that that type of product?
Anyone who has done the research to find their own niche market will never give that information away, they will guard it with their life in most cases.
Bottom line, you are walking into a brick wall and there is no way through it, so you'll have to go around it. The way you do that is through research, research and then more research.
I've never heard anyone say that it was an easy thing to do, but some manage it.