OK, here is the deal with regard to just purchasing the Compression/Rebound kits: basically, this practice is discouraged.
In the case of what Gary did last year, that's an example of where GPSuspension is happy to oblige... but they have a working relationship with Gary's suspension tuning shop (Evolution Suspension).
But for the "man off the street", this install is not necessarily a trivial exercise. It may not be rocket science, but there are special tools involved to hold the cartridge, the cartridge rod, etc. It is easy to dork up a component by using vise-grips, etc, and then you will be out serious $$$ for replacement items.
If you have a legitimate, certified Suspension Shop that you will have install your hardware, sure, they'll sell you the Kits.
But what they want to avoid is having a shade-tree mechanic try to install these without the proper tools, realize they are in over their heads, and then be subjected to multi-hour telephone marathons to talk the customer through the install. They are not a huge shop, and both Dave and Ben are busy all day doing installs or fabricating parts.
Which allows us to have these exquisite components to begin with.
k: