Never even heard of Expedition Essentials, but sounds like I'll be avoiding ordering from them. I've had they same issue with Karst. I really don't understand why companies don't communicate with clients when things aren't available. I've had the same issue with IMO and Optics Planet.
As for knee pads, I wear "non-caving" type pads but they are very functional and comfortable:
http://www.amazon.com/Empire-THT-Grind- ... +knee+pads
Though they are made for paintball, they bend well, are comfortable under my pants, dry quickly and are warm but not hot. The shin part is invaluable and I wound wear pads without them now.They are easy to find for around $40 if you search a little.
The elbow pads here are great as well. http://www.amazon.com/Planet-Eclipse-20 ... elbow+pads
These are what I wear and they are holding up very well so far. Mine probably have around 40 hours of underground time on them and show very little wear and tear.