Great video YG! I don’t know what those grooved things are called either, but you can get something similar – and perhaps even better, because they fit more tightly – by going to an office supply store and buying a pack of side-grip report covers (of the type shown below). I bought a five-pack of these things a couple of weeks ago for another purpose, so they come in quantities smaller than the 50-pack shown below. The four G40 panels have a total of 6 joints (3 at the top edge, 3 at the bottom edge), so two 5-packs would give you more than enough of the sliding grips to anchor those joints.
An alternate (and more expensive) solution is to cover your G40 map with a custom-cut sheet of non-glare acrylic or plexiglass (about 1/16 inch thick), which is the setup I have on my table:
http://www.axisandallies.org/forums/index.php?topic=32700.0
This not only keeps the four panels flat and lined up, it also eliminates the problem of the grooves located at the folding points of each panel. It also (in my particular case) allowed me to customize the map with my own roundels while still keeping the playing surface completely smooth, and thus making it easy to tell the difference between the customized default territorial markers and the ones which get added during play to denote territorial ownership changes.