Unfortunately we haven't had spare parts for the long-discontinued 1210 in quite a few years. BUT - they do use the same knobs as our SCF Pedal:
These knobs are collet knobs made for 1/8" shafts - they have a brass insert and the cap comes off the top of the knob to access this. This is the same type of knob used on the 1210.
We don't sell parts direct but you can order them at most TC Electronic dealers - they will be the ones to get you the price.
The part # is 713050011 (SCF Complete knob Dark-grey)
In the US you will find that Sweetwater (email@example.com) or Full Compass (firstname.lastname@example.org) are the easiest to order through, but you could also try local Sam Ash or Guitar Center stores, although these seem to be on a store-to-store basis.