The rod rest shown is not available in any store as far as I know. I made the first one a couple of years ago and with some friends we made some more for them to use. In fact at the moment we are “re-designing” it to improve it. It's easy to use if you feel you need more than one ready-to-fish rod at hand.
It is a pointed spike with tubes attached to it in about the middle in which the butts of the rods fit, and on top I attached some Velcro lined with foam. It can carry 4 rods, but that is only because the 4 tubes fit nicely around the spine. With three a gap would have remained. You just push it firmly into the sand and your rods will be safe. But beware: dogs soak reels!