Or tayda electronics for less pricey options.
I just received 4 each of a bunch of knobs in different colors and some 1K & 10K pots (not 100% on the values), seems like decent stuff.
http://www.taydaelectronics.com/electromechanical/switches-key-pad/knobs.html?dir=asc&order=price
http://www.taydaelectronics.com/potentiometer-variable-resistors/rotary-potentiometer/linear.html
If I remember, I'll post a pic when I get home.