I'm looking around for the frictions mentioned in the instructions for this Griner th400 brake VB and just cant find such an animal

they give part number 34304H and oem ref # 24202646


http://extremeautomatics.com/assets/pdf/34G20Xtreme.pdf

 

They don't match the part numbers you list but here are some

Waffled forward/direct http://www.transmissionpartsusa.com/...-00046551w.htm

Tan slotted forward/direct https://transpartswarehouse.com/auto...d-1964-up.html

 

#24202646:

Is one of the GM part numbers for the 4L80E Forward clutch/ Direct clutch Borg-Warner High-Energy (green) friction plates.

These are smooth... so do not know why they are revered to as "Grooved/ Slotted" in your instructions.

The "hard" frictions plates that the instructions mention (stated as: "no longer used") are a semi-waffle type friction plate from a GM/ Allison that are used in the Allison AT540 transmissions.
The other "hard" frictions that are also mentioned, are the "full-waffle" frictions plates from Raybestos/ Allomatic... like the ones in the hyper-link below:

Click Here