a multiplexer will allow you to access multiple inputs with just one input pin on the microcontroller. however, as far as I know you can't get any that can cycle through the inputs with just one I/O pin... but since you only need to access 4 inputs, you could do it with two output pins for addressing.
if you REALLY need it to only use two pins, then you could build another circuit from some flip-flops that cycles through the 4 addresses you need (00,01,10,11) with input pulses from your one output pin. (simple binary counter)
or if you don't mind overkill, bear in mind that an 8-pin PIC has 6 I/O pins, exactly enough to handle the 4 servo inputs, 1 pulse input, and 1 output that you need... and it would be very simple to whip up a program to handle it (and at a 1 uS instruction time with the 4MHz internal oscillator, you probably wouldn't lose any significant accuracy versus a hardware solution...)