Individual fan order possibilities.
Rubber Feet (vintagewireandsupply.com)
Set 6 Replacement Rubber Feet for GE Cast Iron Base - Antique Fan Supply Co (antiquefanparts.com)
McMaster Bulk Order. Take your pick.
Compressible-Stem Push-In Bumpers, for 1/2" ID, 9/32" High Stem, SBR Rubber | McMaster-Carr
Compressible-Stem Push-In Bumpers, for 1/2" ID, 1/4" High Stem, SBR Rubber | McMaster-Carr