Mobiledynamics -
Hope this is a great day !
Glad to read you are using Einszett products - I have also been using them since they first came out, a long, long, time ago..
Pretty hard to beat just the 2 products I use the most - Deep Plastic Cleaner, and Cockpit Premium...
At the Chevron gas station & carwash I used to use when I was Detailing full time for EastSide Bavarian, I would get there really early with a Client`s vehicle to get that part of the work done, and was surprised one day to see a guy come out in a what looked like a full on Hazmat suit to load up the part of the machine in the brick room in the middle of the carwash with a soap solution.. It must be pretty toxic, and with that, perhaps they have to have a license to buy it ??
That might be the answer why it is not sold on line at places we frequent..
Have you ever tried Meguiars D108 Super Degreaser as a pre-wash ? I have done this selectively and infrequently on the most dirty, greasy, nasty, vehicles with a good pressure wash rinse after and had great results..
I just re-read your "not requiring mechanical agitation" requirement, so perhaps this wont work for your needs after all
But it does do wonders to engines and engine compartments, rinses off really fast, does not foam like crazy, has never hurt anything under there, and makes the last part, spraying a great plastic conditioner, come out looking like better than a brand new engine and compartment..
Good luck with your research - hope you find what you want, just be careful, ok ?

Dan F