We do not have any serial displays with blue backlights.
We do however, have some STN-negative-blue parallel displays with white LED backlights, and you can find them HERE! Those look quite nice, and it is our opinion that the contrast and useability is actually better than a module that has blue backlight.
The problem with blue backlights is that the blue LEDs are still quite expensive, and the blue light is not stopped particularly well by the activated LCD (reducing contrast). To get a really good effect, you need to switch to a more expensive FSTN LCD, which presses the price higher. Some manufacturers are putting a couple of blue LEDs in a side-light configuration on an otherwise unmodified STN display, and although it is a technically "blue backlight" LCD, the results are not as nice as you might hope.
The reasons that blue backlights are not very common are the same reasons that the yellow-green LED backlights combined with the STN-yellow displays are so popular: the LEDs are cheap and bright, and the light they make is stopped very well by the activated LCD.
But prices on electronics are always headed south, and that is also true for the blue and white LEDs, so keep watching and see what comes up.