Hi Tom,
On a 4017, none of the pins goes low only at "10" (actually 9, it counts 0 thru 9). You could do this a couple of different ways, though. You could connect an inverter (4049 or 4069) to the output that you want to trigger your one-shot from, then into your coupling capacitor to your 555's trigger. This is probably easiest. If you don't need the extra 5 sections of the inverter chip for something, connect the inputs to V+.
Another (kinda neat) way which could work is to basically make a "diode-OR" gate. Get 9 diodes (cheap ones, 1N4148, etc.). Connect the anode of each diode to the outputs 0-8, then connect all the cathodes together. Connect a resistor (4.7K or so) to ground from all those cathodes. Connect the cathodes/resistor to the input of your coupling capacitor. This way, when any of the outputs 0-8 are high, the output of this circuit will be high. When the counter rolls over to output 9, the output will be pulled low by the resistor. This is a "passive" circuit, no power req'd. (see drawing below).
JB