one PIC12C508 per 12 LEDs
    5 output pins available.
    leds driven in bidirectional pairs.
    3 x 2 = 6 (5 pins drive 6 LED pairs)

Ok, I'll bite.  I thought in a traditional matrix arrangement, you needed
the diode characteristics to avoid hidden current paths.  Having
bidirectional pairs would defeat that, and you'd have problems "sometimes"
(I never quite understood which paths were problems.)  Have you actually
got this working (as implied by "requests for code...")

Thanks
Bill W