Japanese Alpha Gel shown in the video, here is the
Company that makes it (English) and their
PDF catalog. You can probably buy it in the size you need from a third party distributor sold for some other application.
If you search for things like "Sorbothane Seat Pad" or *Isolate-It!* or "Gel Pads"... stuff used for Orthopedic Back problems,
rowing pads,
motorcycle gel seats, etc... you may start barking up the right tree... Similar materials include
polynorbornene, Noene, and Astro-sorb.
Sheets / Pads
Gel Pads (Warning, link not 100% work safe, as pics of breast implants on same page/site)
After poking about the Inet for Sorbothane Seat Cusions and Isolation/Dampening Equipment Pads, they are a bit on the pricey side... for a 12x12x1inch square block... so I'm thinking, maybe a homebrew solution would be the way for us homebrew types to go.
According to the theory on the
wiki, its a polymere solid with liquidish properties a lot like "flesh"... which got me thinking... a lot of people make their own "
homemade ballistic gel" on the cheap, with the same characteristics.
I have never touched nor made any ballistic gel, so I may be up the wrong tree... but I think if you were to make it solid enough of the right consistency with close to your desired properties, and encase it some plastic seat cushion... perhaps... bingo... you've got a seat cushion you could add on top of any seat, that would increase substantially your comfort and survivabiility.
From Isolate-It webpage:
"More is not better. A large lightly loaded sheet will have a high spring rate and will not deflect enough to provide good isolation. Over compression will lead to short service life. The proper compression range is 3 to 20 per cent depending on the "Shape Factor." Shape factor is the ratio of contact surface (one side) divided by perimeter area. Geometry matters. Small circular pieces and rings "bulge" better than squares and rectangles. "Bulgeability" makes for better isolation. Use many small discs rather than a few large rectangles for best vibration isolation performance. Thickness matters. The thicker the sheet the lower the natural frequency. You need a sheet at least one-inch thick to get your natural frequency down to 10 Hertz. (10 Hertz is your target natural frequency for a 900 RPM motor.) "
So think something super squishy and rubbery like pictured in the video, that will deform outward from your butt... (I'm visualizing a string balloon, how if you squeeze one end of it, it doesn't pop, but moves the pressure to the other end of it) and spread the force of the impact... and shock waves... outward and into the dampening material.
Like sitting on two or three
unfrozen large gel ice pack or a big
Gummy Bear, or multiple little gummy bears in a bag, but with air space around the sides of whatever material to squish outward and deform. I like bags of little gummy bears, so after each flight I could eat my seat cushion which can be bought on Food Stamps.

Just amortize it as a cost of flying. Any restoration chemical or part I can buy on FS for me is a win.
You know if your spine was that egg and your brain that soda can in that video, you'd want it landing on that AlphaGel instead. CHOPPERGIRL for the Technical Win. And you guys thought you kept me around just for the pretty face. Pfft!
Disclaimer: I'm just a amateur restorer and not an expert on anything other than being snarky

Bonus points if you spotted the goldfish, newts, and gummy bears I slipped all innoculously into a thread about aircraft seating design.