Using 555 to generate square signal with fixed duty cycle / variable frequency
You can try varying the voltage on pin 5 - this sets the upper and lower thresholds inside the comparator and if you lower these (by setting pin 5 to a lower voltage) the frequency will increase. I can't remember how much control there is using pin 5 but I suspect a 10:1 frequency range should be feasible.

Unconnected, pin 5 is at two-thirds the supply voltage and if Vs is 9V then Vc will be at about 6V. Lowering Vc to about 2V should be OK and this will get you about 3 times the frequency. Lifting pin 5 to 9V (maybe you can go above) will lower the frequency by about 30%.

Here's what the charge-discharge looks like: -



Pin 5 has access to the point where the voltage is \$\frac{2}{3} V_S\$ - in effect lowering this will also lower the one-third threshold and reduce the "gap" in volts between the two.

I think if you did a bit of googling on pin 5 control you'll get a more accurate answer than mine.