Armavac is sold out 
this is driving me insane.
Legends tell of teams who have modified vacuum impellers to run off from 775pros.
I think 550’s like the banebot 550 are more common. You’ll find if you go look up the maintenance or spare-parts manuals for many common battery powered vacuums that they are powered by 550 or 775 size motors that you can simply replace with FRC motors to make legal.
In the past we had good luck with the Dewalt brand, but I’m sure there are many others.
For instance, I just did a quick search and came up with:
DEWALT DCV581H 18/20-Volt MAX Cordless/Corded Wet-Dry Vacuum
Who’s service part diagrams can be found here:
https://servicenet.dewalt.com/Products/Detail?productNumber=DCV581H
Which lists the motor as:
5140128-48 MOTOR
Now the weight suggests that might be a 550 motor, and it looks like it might be. You won’t know until you go buy one and carefully disassemble it to check. I’m sure doing research on other brands will give you many other options.
We were able to get more parts faster than expected. They will be in stock in a few days. We apologize for the shortage!
-Andrew