You're complicating your problem with the two-column renderer. As I see it, the actual problems are:
rendering 'disabled' items in gray -- a job for the rendererpreventing their selection -- a job for the selection model
Here's a short example of both (thanks to
Jeanette on the
OTN for the code to access a JComboBox's dropdown list). It has a shortcoming in that if the first item is non-selectable, it still appears as the initial selected value. I'll leave that for you to tackle.