They aren't hard too hard to find, here's their site:
http://www.toploaderbinder.com/
I looked into them because my entire collection is in toploaders and I wanted a way to put them in pages without removing them from the toploaders.
Unfortunately, they are way overpriced...there's no way I'm gonna spend that much on a binder and pages when I could buy more cards. I suppose they can gouge a little since they are the only ones making them - kudos to them, it's a great product, I just can't justify the cost.
Maybe ultra pro will make something comparable and bring the prices down a little. But I suppose if a collector can afford to put together a '52-'54 set then they can afford this product.
btw - I've seen them pop up on ebay from time to time from collectors who purchased them and decided they didn't like them later...you can get them slightly discounted that way.