What makes you think they would be common and available for purchase every where? How many radio's do you think Stryker sells? How many people do you think need or want replacement knobs for cosmetic reasons for a Stryker 955 on the Earth?
If your logic holds true we should be able to find knobs for far more common consumer goods every where! Last I checked no knob stores popping up. A lot of Pot Dispensaries and Cigarettes'/Tabaco stores but not a lot of knob stores! LOL
Some of you guys crack me up! I bet no one with an Icom or Kenwood radio are shopping around for knob kits or chrome cover's! None of them would ever think it is reasonable to expect those things to be common and widely available!