It's hard to tell what they are from the picture you gave the link to, it's far too small. But RS Components gives 19 hits on 'thumbwheel'.
If the ones you're looking for are 5cm wide, that sounds VERY unusual, the main reason for thumbwheels is their small footprint.
I'm presuming you're looking for replacement ones for the picture you posted?, it's quite possible they were custom made ones (or long obselete ones?), have you tried via a spare parts route?.