Peeron does not list these as being in the Education Resource Set, but mine came in that set and are pictured on the cover sheet.
They are also available at Bricklink:
http://www.bricklink.com/catalogItem.asp?P=44292c01
http://www.bricklink.com/catalogItem.asp?P=44292c02
Other wheel assemblies that might work are:
http://www.bricklink.com/catalogItemPic.asp?P=4266c02
http://www.bricklink.com/catalogItem.asp?P=41896c02
http://www.bricklink.com/catalogItem.asp?P=41896c04