I could not find an equivalent IC.
I found a little circuit to let more leds flash using 1 flashled.
D7 is a flashled, the current it draws will trigger the transistor to let the other leds (D1-D6) flash too.
The circiut comes from a dutch cirtcuit site.
I think it would be safer to put a resistor in series with the leds D1-D6 to limit the current.
The number of leds is dependent on the color you want to use (red and green are ca. 1.7-2 Volts, bleu and white are ca. 3.5-4 Volts).
Take a look at Bill Bowden's 1.5v dual LED flasher. It's not exactly like the LM3909, but it does something quite similar using parts that you can still get; flashes a pair of LEDs for a year with just one D cell: http://ourworld.compuserve.com/homepages/Bill_Bowden/page5.htm