I know what you mean but I'm not sure where to find replacements. The felt dots are tall and fit tightly in holes hat are drilled for them. They're a lot thicker than your typical felt pad.
I looked at McMaster-Carr. They sell felt in various shapes and grades. I don't see pre-made dots but they may have something suitable to make some out of.
http://www.mcmaster.com/#felt/=yza6sw
Rodney