Hi Creighton,
Think you'll find that only the genuine Dry Fusion restore brush will fit !!
I bought one a year or so back and they are great. Used it on a filthy restaurant carpet recently and it worked wonders when teamed with the 'Restore' chemical from DF.
There was someone on CIU selling a seconhand one a while back - might be worth putting and entry in the sell/wanted section.
cheers, Pete