I am looking for a 320x240 reflective LCD to be able to display data in bright light. I am aware of the Kent Display but I am not really convinced by the 2sec screen update timings. I'd display large digits with updates every 0.5secs.
It seems like you don't really need 320x240 resolution: that display is mostly just 7-segment digits.
You can get old Palm III-vintage PDAs cheap, and they have 160x160 screens that are good in bright light. You can use an app like PalmOrb (either as-is, or customizing it, since it's open-source) to turn it into a serial LCD.
any ideas on where I could get such 7-segment digits?
You should be able to find raw displays through regular vendors like Mouser or Digi-key, or from surplus sellers, but they usually don't have modules with driver circuits (except for digital voltmeters). It'd be easier, and quite possibly cheaper, to buy a used PDA like the Palm that's considered "obsolete" than to make a circuit with drivers. Plus you can do fun stuff like a graphic compass display by writing code for the Palm.
(I just remembered an exception: I did see one module on ebay that I'd bookmarked. Haven't bought one, though, so I don't know how good it is.)